...Kind of an odd way to put it. All DPS in this game are viable; in the very high end raids, some are seen as a little behind, but they're all still capable of doing the content. If you don't want the responsibility of tanking or healing...

I'm going to second the vote for RDM. It's rotation is relatively easy, but also brings a ton of utility to the party -- namely resurrections, and you can give healers MP. And if you happen to mess up and eat an avoidable aoe... you can heal yourself too. But, fair warning, 'helping' heal the tank or such when it's not an emergency will probably annoy healers.