The difference in dps between tank with tenacity melds and tank with direct hit/whatever is 2% at best, more often than not it sits under 2% actually like 1.6-1.8%
The difference in damage taken and hp healed however sits at 4.3%, and this number believe it or not, indirectly affects the group dps because you require less healing and healers could on average use more offensive spells.

To be honest i would go with tenacity or direct hit on your place, as for me i choosed tenacity because its cheaper and i do more dungeons where extra mitigation matters a lot.
Do not go for direct hit if you want to play warrior, because it will be a waste.