The Breton is more flexible, but if you want to be a Mage, I say go all out with an Altmer. Imperials are actually better than both!

I would have to say neither the breton or altmer is my choice. I normally the wood elf as a pure mage. Add on the Attronach birthsign and the struggle begins. Woodelf+Attronach plus enchanted clothing and the magicka pool is just as good as the breton or altmer..
Like Acadian stated altmers are just way to tall for me.
Bretons are just too much like imperials for me also....

For the longest time I didn't like Altmer either. I really don't like most of the Altmer NCPs. I don't like their personality and most of them are pretty unattractive too. So what a surprise it was when I finally decided to make an Altmer because I wanted to play a race I had never played and ended up loving him. He's one of my most favorite characters I've made in Oblivion. I still don't like Altmer NCPs though. Plus with some work I found that I could make him really attractive and yet still elven looking without all the awkward gawkiness that plague so many of the high elves in the game.

Mechanically Bretons are the most powerful race because 50% Resist Magic is the most powerful racial ability in the game. Although at high levels with the most obscenly overpowered munchkin gear (such as 100% Chameleon suits or 100% Reflect Damage) it doesn't really matter what your race is.

I like Altmer somewhat better than Bretons precisely because they are one of the most perfectly balanced races in the game. They are neither overpowered (like Bretons) nor underpowered (like Imperials). And unlike many others I like their snobish attitude. ^_^

Between these two, Altmer. I love the snootiness of them. Plus I enjoy the extreme height. Looking down on everyone is fun. Altmer Apprentice is my favourite build, so weak, yet oh so strong.

:stare:

Permanent abilities (always active) > lesser powers (can be used whenever you want) > greater powers (can only be used once per day).

Star of the West would make a useful lesser power, but as a greater power it's jsut plain bad. And Voice of the emperor is handy, but in the end a custom 100 Charm for 2 seconds spell is better. Or if you're not into Illusion, you can use scrolls or simply bribe people. It's not like there is any real shortage of gold in this game.

Of course it's possible to make a RP character that makes them genuinely useful (like for example a monk who has taken a vow of poverty), but in general the Imperial's racial abilities are pretty weak. It's also true that in the long term it doesn't make much difference (because 100% Reflect Damage makes any character overpowered) and I also think that looks and style are more important than mechanical stats. But that doesn't change the fact that the Imperials have weak racial abilities. They come nowehere near the Bretons' godlike 50% Resist Magic.

Bretons are the stronger overall choice however Altmers can be really powerful as atronach mages with the spell absorbsion canceling out thier weaknesses

Precisely in the endgame everything is negligable.

However in the beginning of the game the one resource everyone lacks is money, and who gets the speechcraft and mercantile bonuses??? WINNING!