Thank you all, I feel I have learned a lot from this thread
It looks like it is going to come down to experience and how hard the content you take on is if the 3% endurance will be worth taking over the damage boosting skills, so while levelling I will likely skip the endurance and go for damage, and if I feel that lack of hp is making me harder to heal than necessary I will spec that back in to give the healers a tiny bit of extra breathing room.
Hp doesn't make you harder to heal per say. Many healers i spoke to prefer healing my sin with good defensive stat and 23k health than a 32k health pool dude that has crap stats since he went endurance>all.
Also, part of your job is also holding threat. That means talents giving very slight tanking advantage like Shroud of darkness might actually not be as good as a significant dps increase, like chain shock (especially since shock is your bread-and-butter threat generator)
When offtanking, I have to watch out not to pull from the MT if similarly geared unless its another sin.