Okay, reading through the affliction threads already posted the advice is to use either Succubus (with Lash of Pain glyph) or Imp (with glyph of Imp) as your pet for affliction. This despite the advantages the old fell puppy would otherwise have - because that is the one pet that doesn't have a damage boosting glyph.
But it seems that all of these were written from a not-yet-level-85 position ? Level 85 brings demon soul (
Demon Soul - Spell - World of Warcraft) as a spell for all specs, and looking over the spell - it's clear that the best demon soul effect for affliction is from the fell puppy (which is to be expected since it's meant to be our signature demon after all). As it gives a major boost to shadow DoTs.
The catch is that it's a cooldown and it only lasts 20s. I am not at all sure that the effect won't be more than outdone by the constant effects of glyphs. More-over the Succubus's effect is actually not bad for affliction locks either - as it's a boost to shadow bolt.
Personally I went for the drain-life-filler rotation over the shadow-bolt-filler - I found damage to be comparable but in cataclysm survivability is at least as important as DPS and healer mana is much more limited so those major self-heals are a huge boon - I can actually tell my healers "never heal me unless I am low on health *and* out of mana".
So that makes the succubus's shadow bolt less than useful to me (and I suspect in time - most afflocks, everything I'm seeing suggests that draintanking is due for a major comeback in cataclysm). The imp effect however is entirely useless to affliction as it's literally a boost to destro spells only (and that means Bane of Agony and Fel Flame is the only spells we'll see an effect on and fel flame itself is mostly only useful to get an instant-cast renew on UA). In short - the imp has no real value with demon soul.
So the real question is - how much difference can we reasonably expect demon soul to make in a fight ? Enough to alter the existing considerations that lead to the suggestion of imp for drain-life and succubus for shadow bolt ? Is the change enough to let the puppy make a comeback ?
There is one other major advantage to the puppy - it gives warlocks an interrupting silence which has in the past proven incredibly useful (if situational) as a way to disrupt caster mobs. Not a primary consideration but a worthwhile one at least on fights where interrupts are known to be particularly valuable.
Do we have any data on the real effect of demon soul then ? Should I rethink my pet choices with it in mind ? Should I stick to the imp for drain life and just think of DS as a boost to BoA ?