I levelled my second group using dungeon finder only and it really speeds things up. Just stand at any vendor in a city, you can port back and forth whenever your bags are full. Your characters will automatically be fairly well geared. You will learn how to tank and heal much better than if you were questing. It does get a bit boring sometimes to do the same dungeons over again, especially if you are in full heirloom there's little challenge. You can try heroics too, some are easy, some are almost impossible (mostly because of the stat squish around iLevel 100 means Trial of the Champion and the ICC dungeons are very overtuned).