In general, it depends on how you want to play your character:

-For magicka builds, Breton and Altmer are best in general, but magicka DK DPS-ers usually go with Dunmer.
-For tanks, Imperial is probably the best, though Redguard is also very good.
-For stamina builds, you can generally pick any race that buffs stam, but races like Bosmer and Redguard are better because the passives are heavily based on stamina buffing and damage.

Races that buff health more, like Orc and Nord, are currently underwhelming compared to the Imperial's passives, and that's unfortunate. There are some racial passive changes coming in the next update that, according to ZOS, should even that out a bit. Of course, having racial health buffs means you are tougher, which is good regardless of class or role. I am levelling a Nord Templar myself, stamina DPS.

Ultimately, ESO is about freedom to do whatever you want, play your character how you want, regardless of what people might think is "best". There's nothing specific in any of the racials that puts one so above and beyond the others that you can't make up the difference with gear and skill. Plus, Templars are probably the most versatile class in the game, able to take on any role (tank, DPS, or heals).

If you can do your role well, then it simply doesn't matter what race you choose. And in ESO, there is always a way.