If you can stand it wait until 70. There are so many quest chains in Northrend with collection components being able to pick and choose which you want to do is nice. On the team I am working on now I waited until I ran out of all of the fast XP quests in BC and was about 70.7, that is with starting outland at 58.

The above about the sons of Hodir chains is dead on right. I made the mistake of skipping some of that when I was leveling simply because I was in a hurry to hit the cap, going back to do it later on I really wanted to kick myself in the ass. You are going to end up doing it eventually, you might as well take the extra few hours while you are leveling and at least get the xp.

Yes the above two paragraphs are at odds with each other as far as leveling speed goes but they are both accurate as far as overall time investment to get the characters ready for end game is concerned which is what really matters.