I based it off my gear at the time. I was still wearing AK Chest and Head pieces, so I went for the Myth Hat and Chest first. But I also made the mistake of upgrading my legs instead of going for +1, which I shouldn't have done looking back. Although I will get my +1 later today, so not too big of a deal.

I would say spend it on the class you plan to play with the most. If you just heal some of the time on your WHM and aren't taking him to Coil, then don't bother.