Right now, Tenacity isn't going to save you most of the time. If you end up dying, you were probably going to die with or without the extra Tenacity you chose not to take (via melds or substitute equipment). So if you're thinking about going for Tenacity because it's gonna make you "live longer", you're just fooling yourself. Here's an example - the only situation Tenacity will ever save you is if you needed an extra 4k-6k HP to live through an attack. Ask yourself how often that happens and then consider if you actually need it or not. Tenacity does also increase your damage by an amount, I think somewhat compared to Determination, so that's something to take into account as well.
Determination gives you a fixed damage increase, though I'm not sure how much it scales compared to Tenacity. The difference doesn't seem to be considerable, though.
Critical Rate used to be the biggest damage modifier, but they did something to the rates and how much damage you do, making it not as big a priority to get any more of it than what you're already getting from your items.
Then we get to Direct Hit, which tanks are only able to get via melds. But the thing about Direct Hit is that, unlike Critical Hit, if you don't have ANY Direct Hit melds in your equipment, you will NEVER land a Direct Hit! Which is ridiculous. In order enable Direct Hits, you NEED to put in melds. And the more you put, the higher your chances, since it scales linearly. And when you DO land a Direct Hit, you will deal 25% more damage. That's HUGE! Especially if you land one with one of your heavy attacks.
Now on average (as in, if you compared every single fight you ever do), the difference between melding Direct Hit or Tenacity won't be the big. But if you are trying to go for high parses, then Direct Hit is GOD TIER and a MUST HAVE because it will allow you to get lucky parses where you happened to land lots of Direct Hit attacks. And since doing the highest potential damage is all people seem to care about, that is why they tell you to go for Direct Hit.
In other words, if you're going for high parses, get Direct Hit. Otherwise, I don't think it really matters what you get in terms of damage, so you might as well just go for Tenacity.