I feel kinda bad that this is a little bit of a "who should I faceroll?" post, and I don't really support facerolling, BUT my experience, the melee scene in MOP is a much closer race than before, with no melee class sooooo far in the back unable to beat anything (remember wars in cata?) and you can faceroll is you wish, but what if you pick a feral druid and hate it? What if you pick a DK and feel unbelievable shame at picking the class that almost ruined wow (im not mad bro i swear).
What class do you enjoy playing? Don't just blindly faceroll, because you won't get a feel for a character for pvp at level 10, you'll have to keep going, which may be a huge waste of time if you hate the class.