60: level up or gear up?

[Jubber]

Yeah quest till you get to northrend then you can mix up questing and instance runs to give you a variety. You can skip a ton of collection quests in outland and only do kill quests and still hit 70 easily. In northrend alot of the collection quests open up chains that you don't really want to miss.
The instance leveling in northrend will help to keep you from slashing your wrists at the number of collection quests there are out there. Northrend instance gear and quest gear will prepare you for the heroics well enough.