I'm a retired priest, but I played priest for 17 years prior. I really wasn't that good, but here is my opinion.
Templar -- With the new changes to AC, and the damage reduction based on how much AC you have, I don't believe Templar is a good choice, even with life symbol.
[0-70] : 2AC = 1% [70-140] : 3.5AC = 1% [140-210] : 5AC = 1% [210-280] : 6.5AC = 1% AC still caps at 280.
Fallen/Avenger - I believe these are your best choices, in terms of min max. Speed is great! Smart/Evasion is also a great choice. Depends on your rare setup, and play style. I'm pretty aware of my surroundings, so I don't usually get caught in blood light from mages. My overall choice is Avenger!
I think it depends on personal preference and play style as Brandon said it.
With recent changes to dual symbols and revision to ac, speed, and life rare, my advice is to go Avenger or Fallen. Due to speed bonus. Speed is king now. Between Avenger and Fallen, I personally prefer Fallen since you could theoretically equip your priest with the follow setup: G20 ac G10 wise G15 speed G10 evasion G10 smart or ~G9 life or counterattack
Avenger is great option too since you could get g15 smart. However, I personally think smart rare is not necessary due to: 1) People having luck spell from priest dual symbol 2) LUCK stats increasing hit accuracy 3) Accurate rare With high enough speed, and good ping + skills, you should be moving around fast enough and not getting hit so often. From my experience, I died more often to stray and invisible blood lightning spells, so that's why I prefer Fallen.