boosting will be your fastest bet, if you really just want to get to level 60 as fast as possible. If boosting is not an option, then questing will be faster than doing dungeons at the normal pace, however if you hate questing, then you should definitely level through random dungeons. Also I think the 'instant queue' idea depends on your battlegroup. On my battlegroup healers and dps wait at least 15-20 minutes, sometimes much much longer during off-peak hours and in lower level brackets, but tanks are instant.