It's tough to say. It really all depends on if the more dominant faction has the motivation to play along with
you. If they do have the motivation to play along... at what point does it get boring or frustrating for you when
your less populated faction allies cannot give you any reinforcements?

I think Kil'jaeden is actually the highest populated PvP realm with an almost perfect balance. Unfortunately,
even KJ sees very, very little world PvP (most likely because of zerg guild Ruinous). In fact, today they crashed
(or came very close to crashing) Kalimdor thanks to their raid on Orgirmmar.

I guess you have to actually do some research on the realm(s) you're looking to possibly roll on and see if
there is anything exciting going on. Unfortunately, everyone is most likely being a bum and just sitting in their
main cities twiddling their thumbs.