I'd have to say UD........... as a mage, expect to be feared a lot....... and as UD you can sit there and laugh while they spam fear and nothing happens...also cannibalizing in combat is always nice.
no, Goblins are definetly best for D. with rocket jump and blink, you can weave in and out of fear range of any warlock, get you away from priest looking for a fear, (essentially ruling out undead), and assuming you are in a premade, counting on being a belf for the passive resistance is hardly relevant for a defense either, since you won't have any trouble keeping up with a kiting D (assuming you DO get locked in a poly).
for offense, again, goblins are a great class simply because, well positioning is important. always. The best advice any mage can ever possibly be given (besides watch how i play
) is learn to position yourself.
however, you will be subject to a higher deal of polymorphs on the O, (probably), and the group silence is very viable indeed.
i would run troll on defense just because of berserk faster frostbolts mean more CC. you dont need to be undead becasue like no one runs a lock in premades and if your getting caught by priests fear then your garb.