Personally, I prefer to mix some of the stuff up. Tanks can chain dungeons so easily its impressive, but you get bored just as easily. Specially since low level dungeons are too slow paced, you don't have the stuff that make your class interesting yet.
On the other hand, FATE farming in an empty zone can be just as boring. Which is why I do a bit of each, along with some hunts.
And if you take your time, and level across several resets, the Challenge Log also is an impressive source of XP. You just have to be careful to see the warning pop-up, telling you "X challenge is almost complete", so you direct the XP to the desired class.