I'm level 44 and I do what I think is a pretty even balance between Coerthas FATE grinding and Stone Vigil (curse you, Ancient Sword!!!!). I prefer FATE grinding because of the GC seals... but I also like doing Stone Vigil because it gives me Tombstones. At the end of the day, however, you do whatever you want to do.

I disagree with the idea of nerfing FATE xp. If you want S-E to nerf that, might as well have them nerf storyline quest XP while they are at it, since from what I've seen, FATE's give out as much XP as a storyline quest... for what amounts to just about the same amount of time and effort. But yet, I don't seem to see people calling for a nerf of storyline XP. Strange observation there....