Both classes has their ups and downs,

Necro by far can solo better and all the way up to 60
Depending on your play style they can do lots, from pulling,training,charming undead, DMF and twitch.

Mages will have more group dps, mod rods, pet tanks , CAll of the Hero is one of the best spells in the game, people joke about becoming CoH bots but level 60 mages can do quite of bit dps


As far as epics go they are both on the rare loot, but that does not mean you will never get it