Goblin starting experience, by far, is the longest. I don't think you can go back either; so what if you grinded to 19 before you started getting green quests, then did them all? You'd have waaay more chances at epic rolls than running around Kalimdor and Eastern Kingdoms cherry-picking the...
Versatility on a blue Riverpaw Mystic Staff (10) is lower than that of a blue Foamspittle (13). I think that confirms that an epic Riverpaw Mystic Staff would be worse than an epic Foamspittle, although I might be wrong.