Some Final Smashes require aiming, some require being close by, others you can activate instantly, another requires button pressing to make it stronger, and some are just plain cheap, or even at a certain position.
Aiming: Mario, Link, Samus, Marth, Zelda/Sheik, Pokemon Trainer, Ganondorf (could fit in close by as well), Lucario, Toon Link.
Close by: Kirby (if you're a far enough distance, you won't get sucked in), Luigi, Meta Knight, Ike, Olimar (helps to keep foe stuck in the ground), Captain Falcon.
Activate instantly: Fox, Pikachu, Mr. Game & Watch, Diddy Kong, Pit, Falco, Snake, Peach, Yoshi, King Dedede, Wolf, Ness, Bowser, Wario, R.O.B., Lucas.
Button pressing: Donkey Kong (pressing buttons makes it stronger, could fit in activate instantly as well).
Just plain cheap: Sonic.
Certain position: Jigglypuff (you need to be in the right spot to succeed with this one (could fit in activate instantly as well).
I'm sure some could be placed better but this is how I see it. Pikachu, Fox, Falco, Wolf, and Mr. Game & Watch could fit into the cheap category as well. It just depends on how you see it.