Alpha Omega? Obviously as it was built meant for PvP. Necromancer just has a high sustainability, which wont get them too far with PvPs. Alpha Omega has a high output of damage (Burst) which is really good if you want to eliminate a target fast. Also it has the stun, "Maul". Does that answer your question?
Ugh I can't read, I thought you meant PvP. But PvE, it would be necromancer, as I said above, due to it's overpowered healing that sustains him for a very long time.