Hey Leoqal,
You could try Korgath alliance if you're interested in doing arenas. 3v3s are pretty much a daily occurrence and games are generally exciting. It's competitive.
If you're looking for a small tight nit community with a mixture of pvpers, grinders, new players and veterans you could try Vashj or Moonguard. Both servers are quite active and players there are friendly, helpful. Most people here are quite welcoming and come across as not being elitist.
If you're looking for a big server with lots of people online, try Aerie Peak alliance. Just be warned that large pop servers can feel crowded and impersonal, especially if you're rolling there for the first time.
This being said, sometimes people prefer to play on an unpopulated server. Flying solo is fine and can a be refreshing new start. It will also help you obtaining items like Fishing hat, Dread Pirate ring and Arena trinket because of lack of competition.
EDIT: All are US realms