Guild Wars 2

I have a full set of ascended gear on my condi thief. I am kinda done with the fractals. I was wondering for defensive purposes should I put in toughness or vit infusion(which is better?)? Should I just keep the agnony no matter what?

thanks

Depens on what you want to do. For PVE those slots do not matter you either dodge or die. For WvW get vit.