I use Royal Authority constantly. There's not much point in spamming RoH if you are already holding a large aggro lead over the rest of your party; the potency on RA is far higher. The other three are a little more selectively useful. In dungeons, I use Sheltron a lot on trash packs for the mana restore, and it's great for single-hit physical tankbusters (like Heavenly Heel in the new EX trial). Divine Veil is a little bit of mitigation for whomever is nearby you. It's nice to use any time you know that the party is going to take some AoE damage; the problem is that you can't just pop it and have the mitigation be active. You have to be healed by someone besides yourself with the buff active in order to trigger it, which takes some of the control of when it goes off out of your hands. Clemency I use quite a bit, though usually it's covering for bad healers (or dead healers, or the complete lack of healers) or when I'm solo.