For Heroic Uldir, from my experience:
- Taloc - Only really tried this as Affliction since there aren't too many adds and quite a bit of movement during the add phase.
- MOTHER - Aff is pretty much the only viable spec on this fight as there's a lot of movement. You also want Absolute Corruption on this fight if you're assigned to move to the other chamber early.
- Fetid - This is essentially a single-target fight with some two-target cleave happening every once in a while. From the nature of the fight, one might think Desto, though sim'ing and looking at wcl clearly says otherwise - Destro's overall dps seem to be too low. Go Affliction here.
- Zek'Vok - Demonology! This is essentially a zero-movement fight if you play it smart with your teleports and gateways. I actually had a lot of pulls on this in several different PUGs before I finally killed it. The usual PUG strategy for this fight is to have everybody spread out for Eye Beams and stack up for adds. However, if you place your Demonic Circle at the edge of the room, then you don't have to spread as you can quickly teleport if you get Eye Beams. For Rolling Deceit, use your Demonic Gateway then quickly run away from it. You can actually turn this into a mostly zero-movement fight with smart use of your insta-cast spells. I had several groups where I was clearly out-dps'ing all other Warlocks and also most Frost Mages although some of them had higher item level. Extra Bonus: you can actually get quite a decent burst when using your Grimoire combined with your Demonic Tyrant and DPS potion and pretty much instantly target switch. Super useful if somebody steps into one of those puddles and you have to quickly burst down that add.
- Zul - That PUG I was in when I killed it used the "zerg strategy" (*), so I had to use Affliction for highest single-target damage. If you kill all the adds, then using Demonology might actually be best, though I haven't tried that yet.
(*) You pop BL and all your CDs on pull and tunnel boss to phase him quickly, adds are CC'ed and must not be touched until P2 - this requires high dps or you'll wipe. The RL said he'd kick everybody doing less than 12k during that phase and I was quite happy that I just barely made that.
While I did kill all the bosses, I don't have enough experience on the other ones to really comment on what strategy is best for them - I was merely happy that the group I was in was able to kill them at all.