For XP I'd suggest quests. I was doing instance grinding before but after doing some quests I was getting way more XP. With instances I was getting around 60-80k xp/h. With quests this went up to around 120k xp/h and they're way easier while boxing. I liked instance grinding when I was doing something else in the background like browsing/watching movies but from XP standpoint questing seems to win though. James leveling guide was also pretty good help.. either that or I'd look up stuff on wowhead.