I've been pondering this on and off for a bit now. the only alts ive been able to really max level were ones that were very similar to warlocks in some ways (hunter), or were new enough to interest me at the time, but have mostly fallen by the wayside after i hit max level or are only using them for professions (monk).
I'm trying to decide between shaman or a rogue. I know leveling a character is mostly trivial but the early levels i get bored with it so the option to do a free one is kinda welcome. I wouldnt have paid for it otherwise.