I ended up reforging to crit for heroic ultraxion. I lost 9% haste for roughly 6% crit. When I reforged the haste to mastery, I gained 8% mastery. All and all, it's pretty clear just based on this that haste is the best throughout put stat - it doesn't rely on chance, affects all heals, and gives the most benefit point for point. Anyway, doing some calculations for ultraxion specifically, between crit and mastery, as haste doesn't help with a holy radiance rotation, crit seems to win.
Say HR hits for 5000. That makes the ticks roughly 1000 (by my math and heals). The 8% mastery I could get only affects the 5000, meaning it gives an additional 400 healing per holy radiance. The crit, however, affects the entire 8000 (assuming 3 ticks). That means the 6% crit adds an -average- of 480 healing per holy radiance. In addition, the more ticks you get, divine favor, lust, and to the extreme, the blue buff, the more crit pulls ahead. With all that haste, crit gains 60 extra healing per cast of holy radiance for every additional tick. It doesn't seem like much, but it adds up, and with real values and the +3% crit effect meta, it can make the difference between a death or a kill.