My best team? I don't exactly remember, but what I do is that, at one point, I was pretty satisfied with having Blaziken, Gyarados, Skarmory, and Chansey together, as they were all able to cover each other pretty nicely. Former two were sweepers, and latter were walls. Of them all, my most favorite member was probably either Gyarados or Blaziken, since they were the only ones I've mostly used when battling opponents. Did use others, but just not as much.
As far as my worst team goes, that's probably have to be in my first run of Ruby, when my team consisted of only Blaziken and a couple of other random Pokémon (for HM purposes). It wasn't bad, per say, but it just wasn't well-balanced. In-game, it's great, but when going up against a friend, I'm sure they would've had no trouble taking me down.