[baalzy]

At the higher levels you won't be using nearly as much conjuration. For snare you're still using Dooming Darkness because you're after the snare effect, not the damage component. It's also possible to cast dooming on a unsnared mob from max range and have it land before they start smacking you. Our other DoTs are much better for dealing damage due to lower resistance rates and better mana per damage ratios.

Venom of the Snake (lvl 34) is probably the best conj. based DoT we get when you compare its relative usefulness to the mobs you're fighting. At this level you're fighting mobs whose HP is low enough that your pet is going to be ripping them up and VoS will be a big contributor to outdamaging your pet.

Scourge at 39 takes way too long to do its damage for the mobs that you're still going to be fighting (pet will kill the mob long before its full duration) and is less mana efficient than Asystole at 44 (which is both faster and doesn't risk root breaks). Also, in Velious era, Chilling Embrace blows Scourge out of the water (faster & more efficient) and is alteration.

Next Conj. based DoT is Envenomed Bolt at lvl 51 which does nearly the same damage as Ignite Blood but for 70 mana more. Sure, the damage is fast but as you get higher in level the mobs you're fear kiting are going to take longer and longer to kill and you'll be wanting to take advantage of the mana efficiency you get out of Splurt and Ignite Blood while using bond of death to ensure your hp is up to keep the mana flowing.

Plague at 52 is pretty solid efficiency wise and mobs will live long enough to make use of it, although I didn't use it terribly much because I preferred the fact that Splurt, Ignite Blood & Bond of Death are basically unresistable against xp mobs due to resist modifiers. One or two resists from a 300 mana spell will put a big damper on your XP plans.

If you're not fear kiting then there is even less reason, since the Conj. based DoTs have DD components and you don't want to risk breaking root early applying/reapplying those DoTs.

And finally, pets, well.... you don't get much more efficient than a DoT that you cast once and can get a nearly unlimited amount of damage out of. Doesn't seem too prudent to me to spec. conjuration in order to save some mana on a spell you only need to cast one or twice per play session (if you're playing properly). Coupled with the fact that you can reclaim energy on them.

Going Evocation is just a joke if you ask me. You're electing to give up efficiency for your most effective set of tools in order to pretend like you're a less effective version of a mage.

TL;DR Alteration is the best.