Pick your favourite expansion, I know this has been done many times but now that all features, raids and major content in MoP is out, it's a decent time to judge it and compare it to previous expansions.
My ranking would be Wotlk>TBC>MoP>Cata.
Please vote for your favourite in the poll for an overall picture.
I loved Wotlk the most because it had the content I enjoyed the most. Loved almost all raids, heroics but most of all, that was the last time when my friends were all still playing the game and I have the fondest memories of playing with them. MoP is okay I guess but the community is not something I fit into any more sadly. Cata was obviously the worst for a myriad of reasons, in my opinion.