I'd go for non set pieces unless you're primarily doing 2s, in which case both set bonuses are pretty handy and you're more likely to actually see a benefit from a shorter CD on PS. You're also required to play offensively as a healer in 2s so the slow on penance might have an impact.
In 3s, once you fall behind on healing, you'll permanently be behind in healing. That's just the m.o. of a disc priest these days, especially after the 15% healing reduction. I personally go: versatility > haste > mastery > crit/ms.