Simple.
If you'd like your SnS warrior to be optimal when it comes to min/max and be very strong when it comes to gameplay - go Dwarf. As a powergamer and roleplayer both, I sometimes curse the maker for the human + dwarf racial not being reversed 
If you are vain and like to look bad@ss / good - I'd say go Human. Most armors look better on them. And with armor tinting then IMO the Templar armor (human only) is the best looking heavy armor. Something which is a pain with mage + rogue cross-class armor - as the Templar armor CHANGES MODEL with other classes.
For roleplaying, then Dwarf is fine - Human is... boring imo. Despite having more "place in the world", humans feels so vanilla. In my case I always play Tevinter loyalist - therefore human. IMO elven female looks the best for both mage and rogue. Elves also gets their due lorewise.
For min/max regarding combat. Many people argue that the human racial is the best one. IMO dwarf and elf racial are both WAY better on NM mode. This is because /w 25% inherent magic/ranged resist - you can neglect stacking defenses of that type.
Example:
Human racial - grabbing a passive - is +3 will/mag. With will this is 1.5% magic resist.
Dwarf racial - 25% magic resist - equals 50 points of willpower if you consider the attack% stat from other sources.
Edit: Note that physical damage reduction is easy to reduce, the Qunari passive is imo very redundant for a tank. That leaves ranged + magic damage. SnS passives reduces front ranged attacks by 50%. Leaving the only real danger to a tank (when it comes to dying from burst damage) as magic. IMO dwarf passive for a tank is the strongest racial for a warrior in the game. While for mages, elf racial is the strongest. The only case where I'd consider human racial the strongest - is for rogues. For a rogue, human racial is the best one. Except if you want to solo NM as a rogue. For a solo NM run, Elven > Dwarf = Human. Again, my opinion.