Rogues can do either.
In fact, my "canon" DA:O playthrough was as a (female human noble) rogue, they're the most tactically interesting class; with dual blades, they specialise in getting around behind their opponent unseen and stabbing them in the back. If you fancy long range, archers are great support and aren't as boring as you may expect.
My strongest Origins character was a Mage. With a certain Specialisation, mages can become just as adept at sword fighting as warriors, with the added bonus of being able to unleash huge spells in a pinch. Yeah, mages were a bit overpowered.
Actually, the backstabbing thing was almost totally underplayed in DA2. Yes, rogues do extra damage when flanking an opponent, but in Origins they were useless in a straight up fight. In DA2 they can stand toe to toe with most of the games bestiary without needing to work out a path around the battlefield. For what it's worth, I think DA2 got that wrong. Rogues are more fun in DA:O because you have to use your brain, otherwise you die.