Samus - Duo mained with Link in Early Smash 4, and those two were unstoppable together since if one lost, the other would counter the opponent's playstyle. Only reason why I don't have them in Elite Smash right now is a combination of not playing them much because they feel so cheesy in this game, and because I get too overconfident. Playing them today and I gotta say back throw into fair + fair (sometimes delayed to catch air dodge) is so insanely strong. If I get in a team game, it's basically won as long as your teammate can defend themselves since it's so easy to wall out opponents or dodge, and provide support from a distance, and fighting 2 rushdown opponents of decent skill that want you dead is the only kind of threat.
Simon - People respect Simon more than Richter. Funny thing is I only used him one day and my philosophy was "simon only uses whips cause manly, Richter uses items because he is smart". Only to find out that I was doing much much better with Simon since I was using Richter's projectiles like some other zoners, when they are more to give you space or slow the game down so you can use your whip again. Looked up some guides and realized how awesome belmonts can be played and was shocked to realize that everyone just plays them in not only a lame way, but very inefficiently too. I'm actually shocked at how awesome Belmonts are, they are kind of like a reverse Sephiroth because they have similar range and can angle their aerials, but not their f-tilts.
Zelda - One of the characters I played until I lost. Literally 1 game away from Elite Smash. Picked them because my niece wanted to main them, and I was a little annoyed with Zeldas outranging me and not being able to get in on them ever, and wanted to understand them more. They are just as easy as I thought. It's like you are just controlling your opponent's movements.
Pyra/Mythra - I mained Marth in my newbie Melee days, so they felt really natural to pick up. Not only that but Pyra feels kinda like Ganondorf with the emphasis on being slow and read based, another character I play a lot of casually. Swapping characters between matches usually puts me at a huge advantage, now imagine that mid-match. They are so stupidly easy as long as I am aware of how they want to edgeguard me. More comfortable with Pyra due to her range and not requiring as many hits for damage, but sometimes Mythra just doesn't let the opponent breathe ever. Mythra causes a lot of rage quits too and I don't even try to make people rage quit.
Cloud - One of the easiest characters in smash to play, too simple for me to main since he does a lot of the same stuff. Tempted to main him in Smash 4, but Ultimate added a timer which kills him for me because I love the speed boost. Also I prefer Sephiroth.
Robin - Another simple character. OP in teams, he gets a bit harder when fighting fast opponents that don't have to worry about your projectiles but his swordplay is good enough to keep people at bay.
Rosalina - Another character I played until I lost. I may not know any fancy combos, but people really don't know the matchup at all so it's pretty easy to mow people down with her. Strange how most people just outright ignore Luma like it's not even there. Though a couple that did decide to attack Luma, just never attacked it safely so I was able to counter attack and sometimes just take stocks because they wanted my Luma dead.
Ike - The character I use when I need a refresher on competitive play since he's one of the most basic characters. Sometimes I feel like I'm cheating with him because he's better than his Smash 4 self and it feels like no one knows how to deal with him.
Sonic - A character I thought about maining, but I only played him one day in quickplay until I lost and is one game away from Elite Smash. I wasn't camping anyone and I was playing rather aggressively. Sonic's combos are great, he's stylish, and I love going fast.
R.O.B. - I just throw out attacks and they just work, AND he's very versatile with what he does, AND he's heavy with a nice recovery? Yeah he's pretty dang easy. My overconfidence is really the only thing holding me back when I play R.O.B., also Shulk. I dunno why, but every other character I can wreck using R.O.B., but apparently Shulk's experience with mechons just destroys my R.O.B.
Wolf - The second blaster comes out, you drastically increase the salt levels in the opponent even if you never fire it again. Outside of that, he's a very easy character to play and people love playing him as long as the blaster is never seen. Though being greedy for spikes, and Wolf Flashing off because I have muscle memory from side+Bing with Fox to cross up in previous games causes me to SD with Wolf quite a bit.... The power of blaster is so strong though, so tempting to just run and shoot the blaster the whole game so I get into Elite Smash faster so I can swap to another character. I'm not here to make people angry though, I'd rather improve so I don't need such powerful cheese.
Ganondorf - He was one of my better characters in Smash 4 because he was so bad in smash 4 that it forced me to play more efficiently. In Ultimate I just feel like I'm cheating with how powerful and huge he is. He maybe bottom tier, but he can still demolish you if you get overconfident. Ganondorf + Jigglypuff matches are insanely fun because of how intense they are as either side can die from a random hit at any moment. So spacing and getting that first hit is more important than a lot of matches.