Blue Yoshi
Smash Master
Exactly why I don't play in tournaments (or drop out of the tournaments I've joined).I don't want to force people to deal with my lag.
But in my opinion, due to the variety of playstyles, skill levels, characters, and... well, people in general online, I think playing online is a great way to learn the game. As far as playing your best, it's no doubt that offline is when you will play your best (unless you only use the keyboard and not a 64 controller...).
But for the most part, I think online is a great tool for improving.