lol... I will say that you probally won't stick to your first class you pick so get something that you think you will enjoy and have fun. You can always start a new character.
Pick horde or alliance, then chose what class you want since not every race can be the same class.
Some advice I've picked up playing and, toons I've played
Warriors - are usually very "gear" dependant late game, that can be frustrating if you don't raid much.
Rogues - are fun especailly early, but end game they're a dime a dozen and if you want to raid there is alot of comptetion.
Priest - Are always in demand end game, but you better enjoy it. In raids you either the hero or a failure (or atleast a lot of people blame the healers when they wipe
End game PVP rooms are a caster free for all (hunters, warlocks, shadow priest, mages, ect.) not that melee toons can't do some serious damage
Horde side - undead are really popular because will of forsaken.
Alliance side - Seems majority play night elf (cause they do flips when you jump
also if you have any friends playing, then get on the same server because thats the point of the game. and have fun, because it is a game after all...