I second the Minotaur Cave as a good mid-teen level XP farm: It's very close to an inn, Minotaur give okay drops and are pretty straightforward damage dealers so easier to optimize equipment. The spider grotto can be pretty decent gold if one is struggling for the Mino-cave.
Town Hall Quests are great for XP, but Town Hall Quests can require a lot of running around. Bluehall Castle seems the overall best above level 15, but might be too tough for rapid completion below level 15, depending on your build (e.g. agility warriors might struggle to over come the high defense of the deserters).
I like to run a few dungeons of the same type (e.g. tombs, thieves, ice, orc, etc) to minimize equipment change and break up the monotony.
Rumor Bosses seem to give the lowest XP per hour playing but can random drop some decent equipment.