Look at the classes objectively and make a priority evaluation!
Use the forums from nostralius, lightshope, elysium, etc to figure out the expected state of the game once it arrives. For example, on lightshope, on horde side, Warlock, Resto Shaman and Resto Druid are in high demand. It was like this in vanilla too, so if you enjoy one of these classes and plan to do raiding, you're off to a good start!
Gearing up can also have a number of implications for raids and time. Some classes are quicker to gear than others; not to mention raid preparation.
If you want to be the master of economy and grind, look no further than the Mage! Able to accumulate vast amounts of gold.
If you enjoy world pvp and goofing around, rogues (and to some extent druids), will probably be your best bet.
If you want to always find a good spot in life, Warrior, Priest, Rogue, Mage - are your best bet. They have overall best performance.
If you just want to play by yourself and don't give a shit about dungeons and raids. Hunters is your friend.
If you're an edgy retard who want to do what everyone will tell you is a bad idea, then go feral/balance druid, shadow priest or enhancement/elemental shaman. You will always have to struggle for a place in the world, and will always live on the fringe of acceptance. But eh, underdog life <=> thug life!
Warrior is the only tank, so if you like to tank and be everyone's best friend and bitch, a slave to your own sword. Then go for it!