Aight I'll rank those I know and which I try to get whenever I want to(Though I must often just use normal Kirby but I do obtain abilities every now and then)
You should get the ability from
Falco - No comment, you're the god of the match if you obtain this.
Luigi - (Great follow up, edgeguard and you can use them to make him leave the edge(They bounce of the wall so he got to jump from it or such, he can't just hang there) but you're better off with inhale for the final kill kirbycide is so op.
DK - If you get this it's very one sided, as if you land a utilt at any given % you can finish him off or put him offstage with the punch.
Sheik - these can be used but tbh it's all up to you or the match if you should keep it or not.. Great for pressure on shields, follow ups, edgeguard etc.
Doc - These are fun, and Doc's players panic.
Shadowball - so OP, bair to shadowball on mewtwo is so mental.
Anywho if I gotta list it(singles)
Singles
Top:Falco, Mewtwo
High:Samus/DK, Sheik, Pikachu, Doc
Middle:Luigi, Mario/IC, Pichu
Low:Young Link/Bowser, Fox, Link, Jigglypuff
Bottom:Marth, Roy, Ness, Peach, Zelda, Yoshi, GW, Ganondorf, CF
(DK should maybe be with Falco and Mewtwo, or Falco alone on the top and the DK, Mewtwo to high.. and btw the bottom tier is not in any order so CF ain't the worst.)
Teams
Top:Falco, Sheik, Mewtwo
High:DK, CF, Samus(debateable)
Middle:Doc, Luigi, Mario, Pikachu.
Rest:the rest.
(got lazy)
I can post why but i'll keep it short.
In teams,
Falco laser - can keep them at bay, you can save with it and gimp
Sheik - you can save, gimp you can combo and edgeguard.
Mewtwo - Save, gimp, recovery and it's a good finisher.
DK - Great finisher for your combos, and if your teammate grabs someone you can do the puff.
CF - Pretty much just the late option ^
The Middle tier and high tier are really close since most of the middle tiers are used for saving and edgeguarding..
P.S Doc is mighty easy with Kirby, I might even go Kirby instead of CF in the future.