Bowser's seems decent for tacking on damage as he tries to approach or while one of you is landing. This probably isn't as strong against the faster Charizard, despite still being the same move I think.
Link's and Toon Link's are fairly similar in usage, though not quite as restricted by the opponent's movement speed.
Megaman's is only good because of a programing fail whereby the 1 blade limit isn't applied per character, meaning you basically remove his move if you use it right. Otherwise, I don't like it.
Shulk's is great but requires understanding on your part. I need to learn how this works.
Robin's has the questionable trait of limited use. This can work in your favour if you want Inhale back but can't get a free moment to taunt. It is, however, something you have to keep in mind as you play.
Pikachu, Mario and Luigi are always good choices. Doc, however, is a much better hat simply because something about the trajectory and Kirby's different height seems to give him the edge in projectile wars.
Game & Watch's has always been a personal favourite of mine, since it's both a heavily spammable projectile that hits through platforms (except Ferox's statues, sadly) and a close up get off me. It's just as good in this game and seems to work well against its owner still.
ZSS' seems like less of a traditional projectile and more of a tool to buy approach time. It's a great tool in the matchup but you need to get in before you can nab it. I highly recommend the v3 Inhale.
Duck Hunt Duo's is just an extra mindgame to play with them. Useful but, IMO, nothing amazing. Can be funny to use up close to hurt both plays though since it seems to come out real fast.
Meta Knight's leaves Kirby in freefall after use, making it potentially suicidal. I don't see any reason to ever use it over Jumping Inhale.
Dedede's I hear is good because it has much greater range than Kirby's own Inhale and nolonger restricts him to Dedede's sluggish full stomach speed when in use.
Bowser Jr.'s, while amusing, seems too slow and punishable to be of any use ever, I'm afraid.
Wii Fit Trainer's is similarly bad but atleast moves at a decent speed once fired.
Olimar's seems generally to be considered quite bad. I don't get why because it's two of his moves in one, making it faster than its owner's equivalent action, giving you a clear advantage in any ranged fight.
It's not quite the same scenario with Rosalina's Luma Shot but the projectile luma you spawn just ploughs straight through hers. Combine this with its high power and it can really wreck those who are expecting their puppet character to shield them.
Ness' is still as worthless as ever.
Little Mac's is way too signposted.
's copy power in PM was baller). Inhale has its place as an attack without copying powers. Whenever I did copy, I took three things into consideration: 
