So far I have leveled by only doing the story quests, class quests, fates & guildhests. I left every side quest alone so far so that they are available to use in leveling other classes.

I try to save levequests for my DoH classes. Something to note is that I believe you get a boost of around 50% bonus XP when leveling on a class that is below the level of your highest class. In addition to that, you should have side quests, fates, dungeons & levequests (if you so choose). You can also build "chains" when quickly killing monsters which award bonus XP after each kill (bonus is determined based upon the number of the chain). This chain can go higher if you are in a group, which has made forming a party to run fates very popular.

And last, but not least, don't forget that every class has their own, unique hunting log to use for some very nice XP.