I would personally just stack on endurance. Defense, dodge, and absorb/shield all have one major drawback: they only protect from kinetic and energy damage. Bosses like firebrand + Stormcaller, Zorn, TFB, etc. and PvP deal internal/elemental damage, which is unprotected. More health makes you endure longer.
However, this will also be helpful to know:
Shielding is helpful for Vanguards/power techs.
Defense is helpful for Guardians/Juggernauts.
Dodge and especially high endurance is helpful for shadows/assassins.
But remember: in the tanking of today, MORE HP = MORE GOOD!
Oh gods... That person really does not know what he is talking about.