If you want to level in the least amount of time, move to Outland at 58th and to Northrend at 68th.

If you want the easiest time leveling, get flyers (or epic flyers if you can afford it) at 60th and do Outland from 60 and beyond. Ding 70th before you hit Northrend, so you can already have cold flying.

For maximum gold, stay in Outland until you run out of quests. Then move to Northrend and quest both the low zones (Borean and Howling), move to Grizzly and Dragonblight etc. Do every zone, so hopefully you'll have most of Icecrown, Stormpeaks and possibly some of the Basin already at maximum level.

My last team moved to Northrend at 68th, so I'll probably stay in Outland till I'm done everything in Netherstorm and Shadowmoon Valley, just because I've not done those quests in a very long time, so it will help to keep the game more fresh. Plus as an added bonus, I'll escape some of the Northrend colelctions which I despise.