Should I get Cleric's Pantaloons +2. It has 18 healing magic skill. Is it worth upgrading or keep Af3+2 pants? And also if my cure pot isn't cap is augur's gloves still better then healer's mitts?
As Draylo mentioned, you want both. The AF3+2 pants is what makes WHM tick, and is pretty much one of the corner stones of a solid Cure set. Without the MP refund on the pants, WHM cures become quite MP inefficient. You want to use the Relic +2 pants as a enhancing magic piece, especially for Bar-element spells and Shellra V (also as Draylo mentioned) once the pants are augmented.
The order in which someone should gear for Cures should be:
Potency > Skill > MND > VIT
And try to min-max your gear sets from there. Healer's Mitts +1 is the best gloves to heal in if capped potency in other slots offering a total power of 18.5. Augur's still makes a decent Enhancing piece until one can get their hands on
Ayao's gages.