The fatality ring adds no damage to the skills, it only gives you skill points. (I dont think you should be using assassinate)
So if you want those 20 extra skill points so you can use them for things like smoke and expose, use the fatality ring.
If you don't want to permanently have points in smoke and expose and instead want to hotswap smoke and expose rings, use the skulls ring.
I would choose the second option.
PM me and I will do my best to help you with whatever you need.
Skulls ring wins in every way, imo. Don't really need extra skill points for DPS at endgame....
LordOfDiablos: 228 Support Rogue HealerOfEvil: 180 Support Druid ButcherOfEvil: 180 Tank Warrior Proud General of Enigma! 'Lord, you look like a gay detective moose' Limbro, 2015