Long story short, all of the theory crafters argue that for current content mitigation is preferred over endurance for all tank classes. End of story, full stop.
The one potential caveat that I am aware of is shadow/assassin spike damage on Thrasher 16 man HM. It *is* doable with full mitigation mods however. If you want the details for this fight, check this thread: http://www.swtor.com/community/showthread.php?t=646029