My priority has always been cast time > HP/Damage Reduction > Heal power > everything else. Has worked for every game I've ever played, and with how RO2 works my opinion hasn't changed. lol
I know I wont be changing your oppinion at all, in most, if not all cases I'd even agree with you (though I'd personally add mana recovery to the top of the list myself) but isn't cast time sort of a moot point when all Priest/Aco healing skills out side of Heal are instant cast? Heal is a 1 second cast, meaning at Suff 5 you reduce it to a barely noticible 0.9 second cast. While yes, those 0.1 seconds add up, but the bottom line is you'd only ever see that marginal throughput increase if you were sitting there and chain healing with nothing but Heal. The only other abilities that have significant cast times are Res and Sac, and I wont bother getting into them for obvious reasons.