Unfortunately, Breton. They come with innate 25% Magic Resistance. Taking the Lord Stone brings it up to 50% as early as level 1. Do the Agent of Mara quest, and tack on 2/3 Alteration Magic Resist perks and you've capped already. Or you can take the Atronach Stone for the times you want to fight Krosis at level 1. Activate your Dragonskin and become 100% immune to magic for 60 seconds! It is apparent to me that Breton is by far the most useful race considering racial ability and daily power.
Other decent choices are Nords and Dark Elves for their 50% resistance to Frost/Fire, High Elf simply because they run faster, Orc for their x2 damage and defense. The other 5 races are quite underwhelming. The only other possible important thing is the 50% poison resist of Redguard and Wood Elf, but poison is so rare that it really isn't worth taking the race just for that, unless you plan to live among the Falmer. Argonian waterbreathing is useless and the Histskin power is simulated with pausing and spamming potions. Redguard regenerate Stamina is simulated for 12 minutes instead of one minute with Vegetable Soup (only need one Stamina to power attack). Imperial find more gold is useless and the Calm spell can be found in the Illusion tree. Wood Elf 50% disease resist can be overridden by Vampire or Werewolf, or by carrying around 1 Hawk Feather for 0.1 weight to eat if you catch a disease, and the Control Animal power is useless unless you can't kill a bear in the wild. Khajiit, unfortunately, seems to be the most useless race with Night Vision and extra claw damage. The only time I would play Khajiit is if I were playing an unarmed fighter so I could max my damage out.
Warning. These are just my opinions, and I have based them off of game mechanics and min/max perspectives, not lore or looks. Any race will work amazingly well for any situation or build.