I concur that you should play what you enjoy, especially if you're not a passionate min-maxer. Although some builds make the game easier than others, as long as you don't screw up totally (e.g. giving an intelligence-based character strength-based skills) you should be able to manage most fights. You may have to use tactics and preparation more, but then that's where D:OS really shines in my view.
My comrade has much fun playing her rogue and we don't have many problems in fights, although we have no fighter/tank in our party. We focus on crowd control and guerilla tactics instead. It helps that the inquisitor and the mage have three magic schools each, so together with the ranger's special arrows we have every element at our disposal and a huge number of skills in total. Spreading out like this may bar us from the master skills in all but one ability per character, though. I didn't calculate that in advance.
Aerothurge may be good for rogues for Thunder Jump alone. It provides good mobility and may stun enemies, as does Avatar of Storms with its stun-on-hit chance.
Have fun playing D:OS together. It is one of the very best co-op games I ever played, and I'm from ancient days of Commodore 64 and Amiga.
