Low level roulette is good xp. Make sure you are using food as well as FC combat bonus to get bonus xp. However if you see a CCH fate group going, those are fast xp as well.

I do not recommend leves unless you are doing them to get the xp from the weekly challenge log.

Dungeons I recommend avoiding are Aurum Vale once you hit 47. I pretty much fate grinded between 47-50 in NT to dodge that dungeon in the roulette