I would say high elf is way better - I know a lot of people that say bretons are better. However, magic resistance is about the worst thing you can get unless your going for an OP tank end game sort of build. Instead of magic resistance, you want to focus on getting magic absorption. It is really easy to get 80% absorption (just use atronach stone + atronach perk in alteration - alteration is fairly easy to lvl up aswell). 80% is pretty good, you can get to 100% but tbh it is not necessary, you should have enough health/healing in order to take the few hits that absorption doesn't negate ... The reason you should focus on absorption rather than resistance is that you get mana for every spell you absorb. Going to the +50 magicka, this is almost one enchantment (if your not game-breaking enchanting it is only 12 magicka off), this means you can use the saved enchantment to help boost another aspect of your character (often regen or spell cost reduction). I really only use the magicka regen early game if I'm desperate so don't pick altmer for the magicka regen - and I play on legendary difficulty. Even for non-mage/tank characters, I have found that spell absorption is way better than magic resistance.
However, If you don't want the benefits of spell absorption then I would recommend going breton and getting 100% magic resistance (+the atronach stone if ur a battle mage or something depends on what you focus on), because you can still get a nice magicka pool and regen late game through enchantments.
Also, if you are playing as a mage (pure or semi pure), having a large magicka pool is useless and a large waste of perks etc. As (hopefully) you are focusing on getting spell cost down and magicka regen up (you only need about 200+% magicka regen as a pure mage). So going a high elf at the start lets you focus on getting health at the start when you first lvl up - especially when you add the atronach stone and adept lvl robes (and other things).
I do have to agree that this choice does depend on your playstyle of the game - generally speaking though, I would recommend the high elf as the go to race.