I don't play Smash all that much anymore, thought whenerver I do I'm usually relaying on good ol' Mega Man, Pacman, and Sonic what do you mean this is a Nintendo crossover.
Other than those I do love myself some Dr.Mario,Pit,King Dedede,Bowser,Ness and Mr Game & Watch.
I also played Wario for a while, but as much as I tried to find the positives about him I just can't play him anymore without that underlying feeling of disapointment at how shitty his potrayel is, so I don't use him much anymore.
I use Olimar, Rosalina, Meta Knight, Toon Link, Charizard, or Mega Man online (Olimar or Rosalina favorably). In single player (mostly Smash Run because I'm close to unlocking all the Powers and Mii gear) I use random.
Jiggs and Zelda are the only ones I really use. I used Pac-Man when I started the game, and I'm still decent with him. Other I find interesting are Wario, Koopalings, Dr. Mario, and Robin.
I play almost everyone, but if I had to choose I would say my mains would be Little Mac and Kirby. I would say Marth too, but I just found Roy better suited for me.
I main Donkey Kong, and have a variety of other characters I sometimes use. Most notably, I'll use Pac-Man, Mii Gunner when applicable (Lex Luthor, for those wondering), and of course Wario. I don't use Wario too much in this game though, since I'm so used to his Project M version.