I personally feel that endurance and secondary stats are equally valuable so I add up endurance and tanking stats on each mod/enhancement and take the highest total and use those. For mods this is typically the "B" mods.
This is what I do. I don't refer to mods as "high endurance/low endurance" - I call them "high willpower/low willpower". What do I need more willpower for anyways? I'll take the ones with the highest endurance + mitigation, which is the same as "low willpower".
If you really what higher HP get endurance augments but mitigation are better.
Endurance augments are the last place to look for more HP. Changing a "high willpower" mod for a "low willpower" mod gives you more points of endurance than you lost in mitigation.
Even with 25k hp, it's going to take in excess of 10 seconds without any healing for a tank to die.
This is very much *not* true on 16-man. The difference in damage on large hitting attacks is usually 2x and sometimes almost 3x compared to 8-man. Time is often much more important on 16-man than efficiency. Even one or two seconds can be crucial.