Currently the masterwork back item is the best. the only reason why you would get ascended right now is agony resistance and its a long grind and cost almost 100g to infuse. here is a summary of why masterwork is better and rare (guild armor), the exotic version don’t have upgrade slot. After all the grind you go trough it would make sense if the ascended back items had better stats in my opinion.
Berserkers Spineguard
18power
13precision
1%+ critical damage
Exquisite Ruby Jewel
25 power
+15 precision
+3 critical damage
total
43 power
30 precision
4% critical damage
Fractal Capacitor (Berserker)
24 power
17 precision
1%critical damage
Mighty Infusion
+5 power
total
29 power
17 precision
1%critical damage
