If you are looking for a method with the least likely chance of detection (flagging of your account for killing x# of mobs or w/e) I'd switch between IB, grind bot (sparingly) questing and gathering. With IB it will queue automatically for certain instances for you, but like someone said it has issues with some of the instances so you will have to disable them in the settings.. and the best way of course is to make your own profiles, especially if you're on a high pop server or battle group (for pvp). Oh and Recruit a friend! I forgot about it, when I used it my guys leveled so fast that I would have to make myself not bot so they didnt raise any suspicion.. (lol)