Go through everything you like, in order of priority. Exploit the tar out of granted levels. It is quite possible to get ALL classes to 60 within the RAF time period if you know what you're doing, even without logging any insane hours. I've been busy with high level college coursework, and am doing my last run to 60 now with ample time to complete all classes across five accounts. RAF is megalulz.

One thing that's mildly nice to do is make sure one account has all tanks, and another has all healers. During leveling up you get a feel for which of them you like. Leveling is also a good way to explore DPS classes, of course. But remember that many of these you are going to take to 31 (a few lazy afternoons once you know your questing pattern), grant to 60, and not touch again until RAF is done. You will be broke, they will not have all their skills trained...you will still need to make some choices at that point about where your GOLD goes first.

Anyway: have fun, kick ass, bleed RAF for all it's worth before it runs out.