As it is right now, Demonology is 4th, providing a powerful buff and having a very simple rotation, but not yielding very high personal DPS. The less personal DPS is compensated in a 25-man raid, especially if it's caster-heavy. Affliction comes next, requiring hefty amounts of Haste to gain extra ticks on its DoTs - more haste > more DoTs > more Nightfall and Eradication procs > more DPS. Destruction and Demo/Destro hybrid are considered close, with Destruction generally having higher DPS, but hybrid pulling ahead significantly on Decimation phase. All of the bottom-tier talents in Destruction are very strong, but the Soulfire spam is just broken, combined with some Destruction talents and Hybrid being able to double-dip from the 2-piece Tier 7 bonus.
That's pretty much everything you need to know about low-gear Warlocks.
