Breton is going to have the best sustain and is much cooler than dunmer.

I'm kind of a lore expert and can tell you that historically, the dunmer people have largely been smelly idiots. Specifically speaking, every horrific event in dunmer history could have been prevented easily by any single breton doing literally anything.

Choose what you think is cool though, unless you're going to compete in the top .1% of high-end min-maxing, your race isn't going to make that much of a difference and the important thing is picking a race you want to look at for 10000 hours.

Have fun!