My advice is to level as many sets of classes as possible given your current situation (time left on raf, boosting, etc.). Grant levels to wherever you need to fill a gap. This may be boring to grind levels the whole time, but it will give you the most flexibility for the future. What you find fun today, you might not find fun tomorrow. Or, maybe you want to try a new class combo for a change of pace or to try out certain encounters. Doing the up-front work while you have raf, will save you a huge headache later.