I would say Altmer since they have good racial skills as to Magicka and Destro staff. But you can use whatever you like I suppose.

hk11 wrote: »

I don't think there is a soft cap on the Breton's magicka regen.

My breton's magicka regen overcharges. There totally is a soft cap on it.

Please define "mage".
The overall intention of the game is that no class implies any role and each class can play every role equally good.
The current state does favor certain classes for certain roles and mana skills over stamina ones. But that will be fixed long term.

You can pretty much ignore the first passive skill of each race. It let's you reach level 50 with that skilline a bit faster, but after that it is worthless. Hence it does not cost any Skillpoints.

Otherwise you should try to "dodge capped values". Mana regeneration is capped. So Breton Cost reduction (not capped) might be more usefull then Altmer Mana Reg improovement (capped).
The armor/spell resist/elemental resist buffs are a two edged sword. On the on hand it is rather easy to reach caps lategame jsut with gear and those values have to respect soft and hardcap.
On the other hand if you have +300 Spell resist you do not need to get 300 from equipment and can rebalance your gear/skills/morphs accordingly towards damage or surviving.
It depends on too many factors to give a clear answer.

The specific races:
Breton get Max Magica, Spell Resist and Mana Cost reduction buffs. All but the reduction buff is capped (and both should be high anyway with light armor).

Orc's have the Sprint Speed buff wich can be usefull for Ranged Kiting approaches. But otherwise is dead end for mage DPS.

Dunmer make powerfull Dragonknights/Fire Staff DPS due to their damage bonus. They also get some bonus to magika.

Altmer - seem to simply scream "make me a Destro Staff or other mana skill user".
They get max magica, magica reg and (most importantly) a Damage boost. Eveerything but the damage boost is affected by caps.

Personal:
I recently made a Altmer Sorcerer Electro DPS. In part because overload reminds me of a sith sorc from SWTOR.
In part because I heard that the "instantly kill low HP foes" of the Sorc Storm tree also works for Lightning staff and they are the only race to get a bonus to electro damage plus general magika boost.

Bosmer & Kajiit:
Stealth races and classes can be interesting if you plan to use the Stygian armor set - increases spell damage when used from stealth. Normalyl spells are not affected by use from stealth.
Note that several Nightblade class skils count as weapon abilities and thus are affected by the "suprise attack" bonus normalyl reserved to stam abilities.

The other classes have nothing of direct interest for DPS/mana user roles. They do offer some survivability/ability to diversify themself due to higher survivabilities. And like I said before it is possible to reach caps just with gear and buffs.