Best online community to do what? If it's to share pictures and creative outputs, that would be DeviantArt for me. If it's to play games together and update each other on the latest things going on in their lives, that would be Facebook.

I agree though that nothing can beat the camaraderie of a forum community. The force that a united forum community brings is remarkable. Just look at the biggest imageboard there is. LOL

It really depends on some factors, like do you find it useful it terms of learning something new or are you even happy staying there. And it depends on your purpose on joining as well.

Here are some of my fave online communities - For archiving my photos, I use Multiply. When it comes to connecting with my friends, Facebook is just perfect. For microblogging, Twitter is awesome.

Facebook is the best community right now. It has more than 250,000,000 active users.