If you’re looking to min/max and play to the absolute peak of your potential, you should go Human. The weapon skill is absolutely awesome in earlier tiers, but as the progression lengthens, daggers actually become extremely good for tanking. Aged Core Leather Gloves from MC + Death’s Sting from AQ40 will vault your TPS to absurd levels, borderline rivaling Thunderfury on non-Human tanks. This is also done using Fury/Prot hybrid tanking, but that is another arguement.
There is also an added benefit in PvP if you happen to be using a sword like Bonereaver’s or Ashkandi, as you will inevitably run into some Warriors that have random pieces of +defense gear (from the gear itself or ZG enchants), and the +skill will curb the difference in terms of the native 5% hit you need for PvP. If they are breaking the 300/300 flat 60 level defense, and hitting say 320 defense, some sword skill goes a long way in mitigating the chances of encountering a dodge, parry, or miss.
From a PvP standpoint, Gnome is probably best. Escape Artist is unparalleled. But again, Human has a close second in Perception for Rogue encounters (world PvP comes to mind) and Diplomacy (10% bonus rep) reaping the rewards of a quicker Exalted standing with various PvP factions and other factions. Getting an Unstoppable Force 10% faster coupled with the native +5 mace skill will do you wonders in PvP. Probably not noticeable to the average player, but another token to consider in the min/max arguement.
Taking everything into account, Human is probably best for overall min/max.
But, I will point out the fact that player skill is entirely separate from these arguements. I’ve seen plenty of Tauren Warriors absolutely dominate the DPS meters on Horde over their Orc counterparts, just due to the player’s skill. I’ve seen plenty of main tanks that are Night Elf leading the progression charge and raid leading, achieving rank 14, and being regarded as the best player. Laintime was Undead, and is probably one of the best Vanilla Warriors to ever play the game. Monkeynews is probably the best Warrior since in the private server era, and he chose Gnome, yet regularly topped meters.
Point being, it’s always going to come down to your skill level. If you think you are an elite player and have the snuff, roll whatever.
Good luck brother ;].