Where should I go from MoP?

So my intro to WoW was Cataclysm, and I have a lot of nostalgia for Mysts (though I think I may be the only one lol). I was enjoying classic, but I like some of the new features post Cata, but I dislike modern WoW, and I wanna server with an active auction house and-

I'm very picky, apparently. Tl;dr is that I wanna play an expansion post Mysts on a server with an active population, what expansion would you suggest?

Btw, I was playing on Mistblade for awhile but it's pretty dead on there