I personally really enjoyed Hyjal on my mixed team, I did the occasional dungeon and generally enjoyed it. My route was hyjal > deepholm > twilight, did every dungeon along the way.

Now mop is a different beast, at least for me, I really hate questing. I'm currently running dungeons to get to 90, but it's not easy. The XP is not that good, and some of the mechanics are either very hard or completely impossible. Maybe questing is a better bet, I don't really know.

And as luxlunae said, only quest and run dungeons when they are rested.