Disc priest, resto shammy, mw monk, arcane mage, and boomking are probably the fotm ones right now. Outlaw rogues are pretty popular as well. Resto druids remain dedicated flag carriers. Hunters are pretty solid.
My suggestion is to make something you want to try, level it to 19 and get a basic set of heirlooms/dungeon gear and a few key enchants (elemental force, mark of the hidden satyr) and then play games and figure out what you like and what looks fun. Make a new 19 of whatever you choose and make sure you like it, then invest the time/effort into max engineering and BiS gear.