Have I not done this before? I'll go through the entire character list and give general impressions (aside from Miis screw those characters)
edit: actually the mii abilities are tornadothingy (swordswoman), shot put (brawler), and literallySamus (gunner) right? They're all decent/great projectiles so just take them.
Note that if you land an Inhale, unless you want to Starshot to get them offstage, or if it's for a 2v2 attack, you should usually Swallow because it does more damage. You can always use downtaunt to get rid of the power if you REALLY don't want it. I sometimes keep it because I like the hat (like Ness' power)
Bowser: Take it, it's free damage. Basically unpunishable, though Bowser players claim it needs buffs because people somehow punish it. Doesn't seem like Bowser himself can punish you using it on him though, probably due to his large frame and weight.
Bowser Jr: It's a bit slow, and you can't combine it with mechakoopas/clown cars for a lot of zoning, but it can be an alright projectile to force him to do what you want.
Captain Falcon: Inhale is better against him. The punch is only useful for obvious reasons. "For Glory"
Charizard: Same as Bowser, use it. It can even stop Flare Blitz (sometimes, don't count on it)
Dark Pit: it's a projectile, use it.
Diddy Kong: it's a projectile... but it's not very good. It can have uses, but Inhale seems to be pretty good against Monkey Flip (feel free to test this, I would assume the kick beats Inhale but the default flip does not). I do take Peanuts to camp Diddy and force him to approach when I'm ahead/have a banana in hand.
Donkey Kong: Bthrow->fully charged b-reversed Punch is a true combo at 0% and does like 30% damage. The move itself is just good, would recommend.
Dr. Mario: good for gimping and camping, even if he has the cape.
Duck Hunt: very good
Falco: pretty useful
Fox: not as useful, I'd still take it though, it can be free damage when he's far away
Ganondorf: has super armor so if you get a super hard read you can use it and get a very early kill, otherwise I'd prefer inhale
Greninja: Kirby can't followup as easily (he doesn't have the runspeed to true combo out of it like Greninja does, I believe) but it's still very good.
Ike: I believe Eruption has super armor at some point, I'd take it and use it to edgeguard or punish a predictable attack.
Jigglypuff: it sucks, don't use it.
King Dedede: it's literally better, and can eat gordos (why is Kirby's Inhale so BAD AT EATING THINGS COMPARED TO D3/WARIO WHEN THAT'S LITERALLY WHAT KIRBY DOES)
Link: free damage, helpful gimping, forces approaches when ahead, it's pretty useful, even if Hylian Shield can block it sometimes.
Little Mac: it has all sorts of super armor but it leaves you super vulnerable, and Inhale is good against him.
Lucario: take the HECK out of this move for obvious reasons
Lucina: shield breakers are very good in this game, take it.
Luigi: projectile, good.
Mario: projectile, good.
Marth: see Lucina
Mega Man: very good if you use it diagonally or grab and throw it, it's pretty worthless if you just stand there and throw it forward, since his pellets/metal blade/crash bomb all cancel it out.
Meta Knight: it's an aerial kill move. of course you take it!
Mewtwo: if it's like Melee, take it! Hopefully he's not a clone of his melee self though!'
Mr. G&W: take it! projectile! very useful!
Ness: it's awful! It'll never land, and it can heal him! Cool hat though!
Olimar: it's GODLIKE
Pac Man: it's GODLIKE
Palutena: it's actually really good for pressuring. Shoot it at the apex of a short hop it to ensure the reflected shots won't hit you.
Peach: it's a pretty useful counter actually. It can even kill at high %.
Pikachu: projectile, good.
Pit: projectile, good. Why does Dark Pit even exist.
ROB: projectile, good.
Robin: projectile, GREAT.
Rosalina & Luma: it's GODLIKE
Samus: it's GODLIKE
Sheik: it's GODLIKE
Shulk: it's GODLIKE I'M REALLY FEELING IT LOL MEMES
Sonic: it's garbage sorry
Toon Link: same as Link
Villager: pocketing trees or bowling balls etc. can potentially net you instakills. Absolutely worth risking if you're behind. Be careful about getting instakilled yourself when ahead. Slingshot stuff is also useful to grab but can be difficult. Obviously a very useful ability.
Wario: it's basically a much better version of Kirby's ability, thanks Sakurai
Wii Fit Trainer: projectile, good.
Yoshi: eh I personally am bad at using it, maybe if you're good at landing it it's more useful than Inhale
Zelda: actually a really good move, a good "get off me" attack, you're immune to Din's Fire during this move so it makes it easier to dodge, and you can reflect Phantom if they're dumb enough to use that
ZSS: very good projectile obviously
Thinking about it, can you use inhale while doing the dash slide?
No you stop dead with all specials.