Realistically, you'll need a mix of the traditional MMO holy trinity dungeon/raid roles.
[Tank and Heals] For some stuff, you'll need some mitigation and heals to live. [DPS] You'll need decent damage to kill things before they kill you. Also, decent DPS is needed to prevent head trauma caused by your head hitting your desk after you fall asleep because things took forever to die.
But if I had to choose from just the poll options, I'd say DPS because, well, see reason above.