If i were to rank each one it would be like this

1. RPR (AC is a TBN with a HOT with BB that works on almost everything in their kit also a buff and debuff to get more out of your healing)
2. MNK (Got buffs to help with healing even though Mantra doesnt work with BB it does work with Second Wind, RoE is strong and sustainable but no shield so behind to RPR on single target)
3. SAM (play it like WAR and use BB with setsu has buffs as well but when you dont have any setsu or ogi you pretty much NIN in healing though they do have Third Eye to help)
4. DRG & NIN (DRG is great for AOE healing but single is very low incomparison to the others and NIN)
(NIN has good single since they have a min TBN but BB doesnt work with ninjutsu other then shuriken and bushin doesn't work with it too making their big hits not able to heal them but they are faster then DRG so single target isn't too bad)