On the first SSB, I really enjoyed playing as Ness, mostly because his play style was so much different from the others. However, I just don't like playing him quite as much in SSB:M...
I also like playing as Fox on occasion, not only because he has that super-fast teleport attack, but also because that shield of his can make life hell for projectile users. A bonus is that using the shield in mid air also allows him to slow down his fall, so its great for throwing off the attacker's timing. His drawback are that none of his attacks are really strong, and i don't like his recover move (it takes forever and a year to charge up...)
Gannondorf was one of the characters I liked right after I unlocked him, but some of his moves just don't jive with the style of play needed to maximize his potential as a power character. As a power character, it just doesn't make sense to me that two of his special moves are mainly aerial attacks. The up+B move and the down+B move both put him in the air, and that makes him vulnerable. I also think that, while the grand punch is great, there are too few times when you can pull it off effectively. The only move that I have a use for on a regular basis is his flying punch, which is fun. That said, at least Gannondorf has a really cool taunt...
On a side note: i enjoy playing against jigglypuff. To walk in with a character against 3 jigglypuffs (set on x2 damage) and go to town on them... its one of the best things in the world. Jigglypuff has spent over 1500 hours of playtime on my screen, just because i fight them so damn much
...just out of curiosity... which do you think is the best map?