First off, I like the Breton the most. Here's why.
When it comes to Bretons, they are good in the field of magic. While High Elves seems like a more appropriate choice for a mage, Bretons are more of a defensive style and High Elves are open for taking more damage.
What really appeals to me with the Breton is the fact that they have a passive 25% magic resistance with a one-day ability of Dragonskin, boosting it up to 75% no questions asked. However, if the player were to mix this 25% with Magic Resistance, the player then becomes 55% resistant to magic, again no questions asked. From there, if the player chooses to be a heavily armored healing warrior, or a Paladin, the shield ability "Elemental Protection" allows them to to become 105% resistant to magic while they're holding the shield up. This means that any fire, frost, or shock damage does absolutely nothing at all while the player is blocking.
With the 55% if the player chooses to be more towards the mage, this is easily fixed with the "Atronach" stone. Not only does the player at this point have 55% magic resistance, but they also get a bonus of 50% magic ABSORPTION, allowing the player to regain mana when struck with unfriendly spells. (Although the stone also means there's a -50% magic regen penalty, but the "Recovery" skill in Restoration neutralizes that)
Now the benefits of the magic resistance/absorption, that means that ANY magic user (Dragons, Dragon Priests, etc) are completely and utterly useless unless they perchance have some physical attacks that can hurt you. Dragons are useless unless they land on the ground and try to bite you, giving you a critical advantage over them in combat.
I can say the only weakness the Breton mage set up like this has is a strong melee fighter, but that can be countered if the character can conjure and use magical defense resistances.

The game doesnt force you to be a thief if you are a khajiit,thats the beauty of skyrim. be what you want,who you want
The Argonians power to regenerate health is superb, which makes them great tanks.
