Alright I'm sorry for the double post, but I'm hearing a matchup chart is going to be attempted so I thought I should start us off. At this moment, a few matchups are based on discussions we've had but a lot are mostly just from my experience. When we discuss matchups I will edit this post or repost it with changes.
50-50=Not leaning in either characters favor. 55-45=slight advantage/disadvantage but near even. 60-40=advantage/disadvantage. 65-35 or worse=Largely significant advantage.
Bowser -
60:40 Peach:
Basically, Peach outspaces bowser, has turnips to deal with him, can combo him well, and can gimp him well. Peach's dsmash has an ideal launching angle for setting up edgeguards against him since his recovery is so shabby vertically. In addition, her attacks outspeed his and she has responses to bowser's approaches which he is forced to use against her. Bowser, can't combo Peach well, and she can be very difficult for him to hit. He also can't edgeguard her well. He CAN kill her from low, but the fact that Peach is going to be so hard to land strong hits on will give him trouble. But really, do NOT make any mistakes that will caused you to get hit by something like a dsmash of his, his moves hurt.
Captain Falcon-
55-45 Peach:
Big Peach advantage. I believe we discussed this briefly when we were talking about the Falco matchup and the general subject of Peach vs fast fallers was brought up. Peach outprioritizes Falcon 24/7, and her combos are just NASTY on Falcon. If he gets grabbed, Uaired, Ftilted, Daired, or hit by anything that can combo into those moves he will take huge damage. His recovery is also easy for Peach to edgeguard for obvious reasons. Not to mention Peach is hard to grab, punish, and combo; three things that Falcon is reliant on. And if you get "gimped" by Falcon as Peach you're just doing it wrong. Peach's kill moves are abnormally easy to land on Falcon as well, since she can combo into them, and practically. For example, at high percents Uthrow>Fair will work on him. However, Falcon does have some reliable combos on Peach...and they hurt. He also possesses a lot of mobility/speed to get around her spacing and you can't camp him. His Uair/utilt can also give her trouble.
Charizard -
50-50:
When discussing this matchup, we basically all agreed that the ratio was somewhere near even. However, 55-45 Peach, 50-50, and 55-45 Charizard were all being thrown all over the place. Each character in this matchup can punish each other moderately badly for making mistakes, and they can each counter many strategies one another has. I can get more into detail later.
DDD -
55:45 Peach:
D3 can no longer chaingrab Peach, his camping game is severely worse than in vBrawl, hell...even his gimmicky quake hammer fsmash that people were whining about for no reason has little effect on an aerial character like Peach. However, his aerials are dangerous and have big range. Using turnips can help Peach against this. Both characters have trouble edgeguarding one another, and D3 can be pretty hard to kill since he's so fat. Both characters have pretty good combos on one another.
Diddy Kong -
60-40
Diddy is reliant on getting people when they're on the ground. This is a problem against Peach. I'll elaborate more later.
Donkey Kong -
50:50?
I'm not really completely sure on this one, but I don't actually think the matchup has changed that much from vBrawl besides the combos that both of these characters possess, which are both good.
Falco -
65-35 Peach? (See "NOTE")
This is the matchup we went into the most detail about. Peach combos Falco to oblivion like she does Falcon, and his combos on her are lacking. Peach can get past Falco's camping well, and his recovery is easy sauce for him. Plus she can combo into kill moves very well on him. Read our discussion about this matchup if you want to hear more about this.
NOTE: I'VE HEARD FALCO HAS CHANGED A BUNCH IN 5.0. I DON'T KNOW IF THIS WOULD AFFECT THE MATCHUP VERY MUCH BUT THIS IS MY POST ON IT ASSUMING THE CHANGES WON'T MIX THINGS UP DRASTICALLY.
Fox -
55-45 Fox
Fox has a slight advantage here. Foxes lasers can be quite the nuisance, and his ability to land vertical KOs is a slap to the face for Peach. He can also combo Peach pretty well, and he's hard to punish. Peach is also hard to punish though. Her recovery should not be getting gimped here, and his recovery is definitely gimpable/edgeguardable if you know what you're doing. The matchup is definitely difficult, and is slightly in the advantage of Fox.
Game and Watch -
60-40 G&W
Definitely one of Peach's harder matchups. Although, I don't have THAT much experience against him in + so I would really like people's thoughts here.
Ganondorf -
55-45 Peach
We discussed this. Both characters will punish each other VERY hard for messing up, but Peach is harder to edgeguard and has turnips while he is a cow with no projectile. She also can defend well against his approaches. Overall, the matchup is slightly in Peach's favor (although near even) because he has to approach her, and her approaches are also safer to use against him than the vice versa (especially with turnip approaches).
Ice Climbers -
60-40 Peach
I really shouldn't need to explain this. Its the same as it has always been. Peach has always been a sore in the ICs' side. I'm not completely sure on the matchup ratio in +, but its definitely in Peach's advantage, and I'd say 60-40 seems accurate.
Ike
???
Not enough experience to say. Ike can space very well (with a huge disjionted fair that outranges peach's) but Peach has tools to deal with this, and can rack up damage on him. His recovery is also edgeguardable but not too awful. Overall I'd say I don't believe this can be significantly in the favor of either character.
Ivysaur -
???
Not certain here. Ivy has changed a bunch over time so I won't say anything here.
Jigglypuff -
50-50:
These characters seem to have defensive aerial wars for years at a time. Peach has turnips but jigglypuff is very mobile/fast in the air. Not an easy matchup. You just have to know what you're doing.
Kirby -
???
Peach beats kirby in the air, and he doesn't have the aerial tools like jigglypuff to keep up with her, but he definitely has other tools. Not an easy matchup, but not significantly in either character's favor.
Link -
60-40 Peach:
Link may have Zair for spacing, but once Peach gets in (turnips help as usual), and she will, well...lets just put it this way. Link's recovery is trash, and his bulkiness allows him to get combod badly. Still, he is VERY good on stage, and can keep Peach at bay for a long time. This matchup requires patience really.
Lucario -
50/50:
Peach isn't a good character for killing, but she is for racking up damage. Lucario is weak when he doesn't have much damage, and strong when he does. Basically, this matchup has the same concepts as vBrawl. Its all about getting the first kill. If Peach gets the first kill, Lucario will be at 0 and Peach can rack up huge damage on him without taking strong hits. If Lucario gets the first kill, he can rack up damage on Peach and last a while since she isn't good at killing. Both characters have many tools against various aspects of each other's games.
Lucas -
???
I'm not experienced against good Lucases. I can't say.
Luigi -
55/45 Luigi
This guy is annoying but not that bad once you learn to play against him. He can vertically KO you very well. His aerials are really dam fast. He has a big recovery, though its manageable for Peach. As Peach you have to remember to space yourself really dam well, thats basically the trick here. And you MUST punish him if he messes up. He shouldn't be gimping her but it doesn't matter since he can KO her well.
Mario -
65-35 Peach:
I think we may have discussed this for like 2 seconds. Peach absolutely outprioritizes Mario, her attacks (like Nair) will just plainly go through fireballs. His recovery is trash. He can't gimp her. He's bad at killing. This one should be obvious.
Marth -
60-40 Marth:
Its marth's advantage for the same reasons it has always been. We've discussed this, and I really shouldn't have to go over THIS matchup of all things.
Meta Knight -
60-40 Meta Knight:
This one should be really obvious. Seriously. However, from vbrawl to Brawl+ Peach is harder to punish, doesn't have as difficult time killing, and has grown as a character overall. Meta Knight has been nerfed. His upB doesn't have its crazy invicibility anymore, Mach Tornado got slapped, and he isn't very good at killing anymore unless he shuttle loops you (although his edgeguarding is still nuts). Peach is hard to edeguard, meaning she can last longer against him now. The matchup is definitely in MK's favor, but not as bad as before.
Ness -
???
I can't say at all here. Not only do I not have much Ness experience in +, but Ness has also been changed a lot in the latest build. We should discuss this.
Olimar -
???Peach advantage???
Olimar is that character in + that people say is really dam good (true) but no one uses. This matchup was always debated, but was never considered to be in Olimar's favor. This needs discussion.
Peach -
50-50:
Pikachu -
Near even:
Its definitely not an EASY matchup for Peach, but its probably near even. I'm not hugely experienced here.
Pit -
Near even:
See Pikachu.
Pokemon Trainer (All) -
???
No one uses PT. I honestly have no idea. Everyone seems to use one of the 3 Pokemon individually now.
ROB -
65-35 Peach:
I have more experience in this matchup than any other. The key to this matchup is really KNOWING how to play it. Good DI is really helpful here. Peach is extremely hard for ROB to edgeguard with how evasive Peach can be when recovering, and there's also the fact that her umbrella has S-Tier priority. She can pressure him very well, and has great approaches (as usual) against him. She mostly outprioritizes him as long as you space right, and she can juggle him well. Killing Peach is really difficult as ROB. This description is really small and I can get into really really really big detail about this if desired.
Samus -
50-50/55-45 Peach?:
They both have killing problems (although Samus's are more severe usually). They both have good recoveries, but Samus is easier to edgeguard. However, Samus is pretty bulky which makes up for that in this matchup. Samus has Zair to outspace Peach, but Peach has turnips and other stuff. Peach can Nair through missiles. Use a quick ground float nair so you won't get punished when doing this. Overall they go pretty even. Reminds me of melee. However I put this as possibly slightly in Peach's favor Peach she can kill slightly better in this matchup. It is NOT an easy task to kill Peach as Samus.
Sheik -
???
I don't have experience against Sheik in +. Can't say.
Snake -
60-40 Peach:
This is like vBrawl, except he's easier to combo, can't camp as well, is easier to edgeguard, his tilts aren't as effective, etc. Then again, I'm no expert in this matter so I'm not totally sure.
Sonic -
???
All of the Sonics I play suck. I can't fairly judge this matchup, but I don't think its significantly in either character's favor.
Squirtle-
55-45 Squirtle?
This needs discussion. Near even IMO.
Toon Link:
See Squirtle.
Wario -
???
I'm not experienced when it comes to Wario in +.
Wolf -
Near even.
We should discuss this one.
Yoshi -
???
The Yoshi I play sucks. Can't say.
Zelda -
55-45 Peach:
Peach can juggle/edgeguard Zelda better than Zelda can juggle/edgeguard her. Peach also bothers Zelda a lot with her pressure, but you really don't want to float very much against Zelda since she has good anti air options. Zelda can punish Peach badly, and her hits pack a punch.
Zero Suit Samus -
???
There is now way this is a 65-35 matchup. I just don't have that much experience here, and shouldn't judge it. Definitely winnable for either character.