Either... Leaf, from Return to Dreamland, or... Magic! :D From that one GBA game I forgot...
Magic came from two different games if I remember correctly. Amazing Mirror (or was it Nightmare in Dream Land?) has it in the one-time use form, while the Magic you see in Kirby Squeak Squad/Mouse Attack is an extended version which grants it actual attacks, some of which have properties like Hammer!
As for my take on the abilities, my favourites would have to be Super Star/Ultra's Yoyo, Adventure Wii's version of the Hammer (gotta love that Hammer Twirl) and Smash of Amazing Mirror.
Fighter and Sword are my favorites.
Hammer (Though I am fast enough with Ike's Reflect move :P)
My Top 3 Favorites:
1. Ice (Because of Glaceon's Type :P)
2. Mike (Your terrible at singing kirby! :).)
3. Paint (Paint me something!)
My favorites are unique because they spell IMP
I tent to like the abilities who looks cute for me instead of how useful are they C:
But I like to many! My favorite is probably Beam; but I like Bell, Archer, Paint and Parasol a lot too.
I can't really decide of a single favourite, so I'll just make a top five list:
5: Cutter+Bomb (because ninja stars are awesome, especially if they explode)
Runner-up: Cutter+Fire (because fire swords are awesome)
Oh, and let's not forget Hypernova, the god of Kirby abilities.
*Note: All of the non-combo abilities are from Tripple Deluxe.