I prefer Rebirth +Regeneration. I'm sure everyone has their own preference.
Definitely +regen
Regen. The number of +HP/sec you get for Core is not even in the same ballpark.
Blue
American Steele: 50 BS/Inv
Nightfall: 50 DDD
Sable Slayer: 50 DM/Rgn
Fortune's Shadow: 50 Dark/Psi
WinterStrike: 47 Ice/Dev
Quantum Well: 43 Inv/EM
Twilit Destiny: 43 MA/DA
Red
Shadowslip: 50 DDC
Final Rest: 50 MA/Rgn
Abyssal Frost: 50 Ice/Dark
Golden Ember: 50 SM/FA
I tried +HP on my widow to see if it would cut down on those 99% health to 0% health 1 hit wonders in the trials, and it did absolutely nothing.
The only thing I can think of where +HP might be useful is for a MM, since it would be a larger percentage gain for pets.
I only have one last T4 to finish on my Night Widow build and I was wondering which Destiny slot gives the better benefit? Ive tried searching the forums but I cant find a thread that compares the two. Any suggestions would be greatly appreciated.