I have leveled up to almost to 80 (currently 77) with Affliction. I have hardly any down time unless I mess up a pull but even then it is minimal. I think either one is good for PvE so it mainly depends on your play style. Demonology relies heavily on your minion while Affliction relies mainly on your DoTs.
Edited, Sep 10th 2009 11:01pm by rievley