Falco, Samus, Mewtwo, Doc, Sheik, Mario are all good for Kirby and give either spammable stuff or killing power.
Pikachu's is unnecessary but can be helpful. On the off chance he's trying to ultra-camp you it can help deal with the spam with counterspam if you don't feel up to just d-tilting or f-tilting the jolts or wding back into shield or powershielding them (etc) when he approaches backed by spam.
Fox would be good if Fox wasn't super fast and didn't just u-smash you when you jumped to shoot. Or grab you when you're about to land, etc. This is not the case and Fox's blasters are pretty useless. Maybe on his Green Greens counterpick? Even then normal swallow is probably preferred for the potential gimping. To make it worthwhile too much has to be working in your favour and honestly this is Kirby.
Link and Young Links' arrows aren't particularly stellar, even on someone as amazing as Kirby. Swallow is probably better. Maybe for giggles or something but arrows don't help much. They eat through bombs but lose to boomerangs and take a while to charge and honestly Kirby's not outcamping anyone. You could be creative and find a use in some awkward edgeguarding situation perhaps, but it won't come up often.
Bowser's is weird. Kirby gets the flame cancel in each version. So he can do that for tricks. Not sure how practical it is but maybe someone will make some weird Kirby shield pressure technique with it (unlikely).
Kirby gets Giant Punch from DK. While in theory tech chasing with Giant Punch (or just Giant Punch in general) is a sound plan, Kirby's lack of range and speed and DK's general **** on Kirby prevents this from being very useful.
Everyone not mentioned is useless, so situational it's not worth noting, or forgettable altogether.