WOTLK>Everything else. How anyone can compare WOTLK with MoP (Or WoD, are you mad!?) is beyond me. The only explanation I can come up with is you didn't play much of WOTLK because you can't compare them. Don't get me wrong, I enjoyed MoP, it was decent and I've had fun in WoD but WOTLK blew my tiny little mind. It was (and probably always will be) the greatest 2 gaming years of my life. MoP had some good raids (well, one really, and it was OK) but WOTLK had Ulduar and ICC. Ulduar was (for me at least) the best raid Blizz have ever made, it's pretty much flawless. And ICC was pretty spectacular. And that's just two raids, everything else about the xpac was also brilliant.
I'm guessing you barely played WOTLK or just have very short memories.