Hi!
In terms of activity, I believe the MoP 3v3 ladder is the most active 3v3 ladder across all our realms. The reason for this simply being that arena teams are no longer required to do arenas.
In terms of bugs, many still exist and require fixing. Devs have fixed quite a few exploits, but the rate of these fixes hasn't been too encouraging. With that said, 5.4.8 does sound promising, and we will have to see if it will bring this realm to the promised land or not.
You do need to level up though, from level 1 to 90, and then gear up as on retail as well. This may be a bit of an issue for you I'm afraid :/
Best of luck with your decision!