endurance or shield rating? which one should i stack or put priority on?

For optimal distro, you want 4-5 Shield augs and the rest Absorb augs. You'll get all of the Endurance you'll ever need on your gear naturally, so there's no point in auging for other than simple epeen with big hps.

on my vanguard i run

2-3x 18 def / 12 pwr

4x 18 sheild / 12 pwr

and then the rest are

18 absorb / 12 pwr