Imperial: extra health and stam, red diamond is only sort of useful
Nord: extra health, stam and healthy recovery, damage reduction but I'm not really sure how well that stacks with other sources of damage mitigation
Orc: extra health and stam, extra healing received, increased damage
Argonian: extra health and magicka, potions restore all stats, increased healing done/received, poison/disease resistance
So all of them are good for tanking, it just depends on how you want to play. If you go Argonian, you've get a big benefit from popping potions to help your sustain. I usually play Imperial tanks but that's more for roleplay reasons.
Friend: This one has a cool joke to tell. Want to hear?
Me: Sure okay.
Friend: What can a frozen band-aid be applied on?
Me: This one don't know. Tell me.
Friend: A cold cut. Get it?? hehehe
Me:.... *activates Grim Focus!*
Friend: No wait! it's a joke! please!