Urahra

Most active is probably Haense or Oren or something.

As far as best goes, that's hard to determine. You could say that the settlement with the most players is best, but that's if your only going for quantity and not quality. I suggest you look around and see what sorta roleplay niches you're interested in, and find a good group that performs said roleplay niche to stick around in.

Oren, Haense, Elvenesse, Norland, Urguan. These are currently the most active. The best one of course is the Mitzuul Grove, the home of the Kharajyr! 

But for real, what jumper said. I'd suggest checking out the Edict  of Kermesinfels also, I kinda like how they look. They're a secretive group. Maybe the Druids? Why not Halflings?

maybe try dobrov i hear it has an active magic trading community