I would say 1-50 its all Necro. You give up a bit of pet strength for lifetap heals, FD, fear, mez, and very efficient DoTs. Sure Mages will do fine XP wise by finding those solo outdoors targets and mindlessly killing them every 6 minutes, but for a dungeon crawl give me a necro any day.
At 51+ though the surprise winner is . . . enchanter! For three big reasons:
1) Mob HP. When fighting a L50 mob that hits for 140 and has 10k hp with a L45 pet that hits for 70 and has 2700 hp . . . the pet is not going to last long. Enchanters can fix this with slow. If the animation has a burly 1800hp or so, divide that by 0.3 for 70% haste for over 5000hp equivalent. This is ignoring the Rune/Bedlam line too; with Bedlam and slow I tanked the Armsman (L52) myself all the way while good old Gebober beat him down. Basically slow/haste become huge with the longer fights.
2) Summoning mobs. Enchanters have PBAOE stuns and AOE mez to deal with charm breaks against summoning mobs. Plus when the summoner is slowed it almost doesn't count at all. So even with undead mobs to charm the necro is at a pretty significant disadvantage.
3) Power curve. A lot of enchanter spells just keep getting better. Rune IV/Bedlam for 1100 hp at L60 is great, Theft of Thought is amazing, and most importantly: the Leatherfoot Raider Skullcap is cheap enough that if you are soloing you can afford to use it to bail you out of most bad situations; it's like a 200p FD
[You must be logged in to view images. Log in or Register.] Really its hard to overestimate the importance of the WC Cap: without it I think enchanters soloing zones like HS South would be borderline impossible. Even in an a relatively easy area like Chef/Bar I have to be really careful when my cap isn't charged.
All that being said, Necros can still do an absolute ton, but I think they lose a bit of their edge. Velious will be interesting, as from what I hear the vast majority of mobs are either sick MR, or immune to stun/mez. So enchanters will suck there and Shamans will rule.