Well, the only Cleric classes I’ve played are Cleric 3, Krivis 2, Sadhu 1, and Monk 1, but I’ll just talk about Cleric and Krivis since I have the most experience with those two.
Cleric 3 is pretty good on the support side with some really good Holy element DPS. The best skills would be the first 4 you start out with: Heal, Cure, Safety Zone, and Deprotected Zone. Like some people have already said, Heal also deals damage, but obviously you will find yourself using it to actually heal more than attack with it. Cure would be your main DPS skill as it can deal so many hits at higher levels, but the major weaknesses to this skill and Heal is that neither can hit flying enemies, and their range is really small. Safety Zone is a great defensive skill to have since it can completely block damage for a set number of hits, but it can’t block status effects and you can also get knocked out of it. Finally, Deprotected Zone is helpful for STR-based classes.
Krivis is kind of bad on the support side, but they do have an amazing DPS skill called Zaibas. Zaibas is a lightning element spell that also has a ton of hits the more you level it up and it can also hit flying enemies. Personally, I think it’s currently one of the best magic DPS skill in the game despite its long 30 second cooldown and slightly short range. As for support skills, Daino and Divine Stigma are the only ones really worth taking, but Zalciai has some uses if you get its Magic Amplification attribute.
As a little side note, combining a high level Cure and Zaibas will most likely result in extreme overkill. I’ve been able to destroy every quest boss in a minute or less, all the way to Lv 135, with only these two skills. Just having them made the entire game look extremely easy, but I expect some kind of nerf in the future. The best part though, is that my character only had Lv 10 Cure and Zaibas, and was a STR/INT build that was aiming for Monk, so I can only imagine what it’s like having a Lv 15 Cure and Zaibas with full INT…
Well, I might have went a bit off-topic there, and I’m not sure if I answered your question, but that’s pretty much what I have to say.