I play a mix of King Dedede, Pokemon Trainer, Pikachu, Metaknight, Kirby, Mario, Link, and C. Falcon. Note that I don't own the game, but can use any of the above to compete at least evenly with my friends who do own the game. Of course, this may be more an indication of their skill than anything.
With Dedede I weaken from a range with forward tilts and Waddle Dee's, then lay on the hurt with fairs, bairs, down/up smashes, and occasionally the Jet Hammer or a forward smash. The Final Smash leaves something to be desired, but with the powerful aerials I can usually break it.
With Pokemon Trainer I use Squirtle to take on most of the ranged characters by dashing in with his up smash into a Surf. Anyone that needs to be at close range, C. Falcon or Kirby, is susceptible to Razor Leaf poking and Bullet Seed general winning. And Charizard is my bruiser and my main protection against other bruisers, he uses fair to advance, then uses Flamethrower to damage, and finishes with Rock Smash. All three are great at getting the Smash Ball, and the effect is decent when aimed well.
With Pikachu, for me, it's all about Thunder juggling. I still know how to use his other moves effectively, but I love keeping the enemy suspended in mid-air while Pikachu adds his "Pika!" with every strike, such a great annoyer.
With Metaknight I play a standard weaken with normal attacks/neutralb then finish with up b/down smash and Wall of Pain if necessary.
Kirby's my favorite close range fighter. He gets right in people's faces and beats the crap out of them. Advancing got a whole lot easier with his new dash attack, as well as the improved/changed aerial hammer attack. His final smash is alright, but there are better ones.
I play Mario very close range 90% of the time, but I occasionally switch to Fireball sniper mode to score some hits and generally annoy my opponent. All his aerial attacks are great, and the Cape needs no introduction. The FLUDD seems a down grade from the Mario Tornado, but it does have some limited uses.
Link I play as very annoying and ranged, hitting with bow, boomerang, and bomb before closing in for a quick smash/dair kill. Standard Link.
With C. Falcon I weaken to about 30%, then start setting up exclusively for Falcon Punches. It's more of a comedy strategy, but it has scored me early kills on numerous occasions.