Well, what is "best" depends on what you are looking for. Do you want sth that is easy to play, sth that is versatile or challenging and interesting? I always try to create characters that somehow mirror myself. But I will explain this a little further down here:
If you want to go for the "easy" character, go for a Nord, Orc, Redguard or Imperial and do a simple warrior. And by simple I mean SIMPLE: No 2-handed weapons, no magic, no fancy experiments. If you invest into one-handed weapons, heavy armor and blocking combined with some shouts and a follower, most fights will be really easy.
Smithing will provide you with really strong weapons and armor that are way ahead of your actual level.
A follower like any of the housecarls is a nice addition which can carry stuff for you, tank and dish out serious damage. You could go /w Lydia like 99% of us. You can provide her /w armor and weapons that you made for yourself since smithing is really advisable for any warrior as mentioned above.
Never underestimate blocking. It can stun-lock your enemies almost 100% of the time.
For a mage go /w a Altmer, Dunmer or Breton. I think a mage offers the most versatility since you get to do basically everything you want to. You can use the elements to strike your foes, conjure Atronachs to your aid, use bound weapons, cast armor spells, use detect life/muffle/invisibility spells for sneaking and so on.
While a mage requires most thought during fights imho, I think it's also most rewarding. You don't need any equipment really. I have a now level 40 mage and he's perfectly fine with his Adept Robes/Hood. Get a Frost Atronach to tank for you and DESTROY everything in your path (jk).
For sneaky assassins I'd recommend Bosmer, Khajiit or Argonians. It requires patience and a high amount of overall awereness, but will be very fun and interesting.
Get Assassin's Blade and a generally high level of Sneak and your ready to go.
In conclusion the simple warrior is the easiest to play, but I can't identify with such a character and don't find it particularly interesting... In the end it comes down to any of the archetypes (warrior/thief/mage in this order) being a good choice for beginners. The more you strife away from these models, the more unique and challenging your gameplay will be.
I'd advise you to try and make the character that you find most interesting work. I have done this with my Dunmer Illusionist Assassin. He's a level 4 vampire 24/7 and only invested in stamina & magicka, which comes down to 40(!) max health (because being a lvl 4 vampire reduces your health by 60). In return it offers a really wide range of tools to use. It's really hard to play but completely OP once you've mastered it