Ok, I will address your query in terms of gvg (based on videos only, as I have yet to participate).
CLERIC
This is your basic class. You can deal damage, but I feel your skills are better served to support. With that in mind, here are my though on some skills you might not think about.
[fade]'s obvious effect is to reset aggro. That doesn’t really exist in GvG. The other part of [fade] is the immunity to magic circles. So long as you don’t deal damage, [fade]'s immunity will not go away and will last its full duration. I’m GUESSING [fade] 10 would be good to maximize the uptime on this immunity
[heal] will no longer be enough at 10 given the increase in people you interact with. In the usual dungeon content you only have 5 players to think about. That’s not the case in GvG
[safety zone] might actually get you killed because it is a giant sign saying “kill everyone HERE”. The more people standing in the zone, the faster the blocks get eaten up. The more people hitting the zone, the faster the blocks get eaten up. Much like how the crazy tree boss from missions will completely erase a lv 5 [safety zone] because 1 volley of 5 apples hitting 5 people each is is 25 hits vs 10 blocks. GvG will certainly have more people in the zone and hitting the zone.
PRIEST
Personally this class is a trap for current content. However, with the rise in players interacting with you, the value of your skills increase.
[mass heal] will heal more people.
[revive] will affect more people.
There is also the future buff to [blessing] (and possibly [sacrament])
KRIVS
I really hate what I’m about to say but might just end up as support via [aukuras]. I love the idea of the skill but I hate it level progression.
[aukuras] 15 is a -15 sec HP regen time and an accuracy debuff. It sucks that you need 15 pts in [aukuras] for -15 sec vs 1 pt for -8 sec but it is what it is until IMC changes it. This is a sample oh how potent hp regen time can be when fully invested in.