I am playing a shaman at the moment. I love it once you hit 18 it really picks up. Can heal over time, dot, haste ppl, all kinds of good stuff. I picked wolf form shaman and it is rocking. I also hear that necro is psion are great but they don't pick up till later in the game then shaman.
If you always wanna get a grp though I would pick a tank class they seem to be the highest in demand.