I like doing it by doing the quests though and this is where Outlands and Northrend really fall down.
Both have a very linear progression - in some areas there isn't even much difference between Horde and Alliance due to neutral bases. Also unlike Azeroth there is only one real quest progression line which is to go through the areas systematically - Azeroth has at least two differing paths per continent, making four in total.
Also the quests themselves are so benign and take far too long to do, and there's far too many of them. It takes me roughly as long to do 60 levels as it does to do the next 10 and then the next 10 after that. There's something really wrong when that's the case.
I hope soon Outlands gets at least a revamp to just two or three areas of about 60 quests maximum each, or better still just disintegrates and does everyone a favour. In particular, whoever designed Netherstorm, Shadowmoon Valley and Blade's Edge Mountains needs a public flogging.