Before the the big patch the fastest and easiest way to level was to do fates in a fate group. While fates are still a good way to level on my server the amount of people doing them is lower than before and thus it takes longer to do them. My first class took quite some time to get it to 50 because i did many quest.
After the big patch i leveled a WAR to 50 in a few days going for 5 levels day after i hit level 30, getting a character to level 15 doesn't take much time, just do the Hunting Log and any Fate you can do.
After you hit 16 you should do your low level roulette everyday. Since the patch doing instances are good exps and tanks normally have zero wait times. Another good way of making exp is to do escort leves. For example i did the leve "we are missing one of our naturalist" about 60 times (level 45+). If you ignore the mobs and just run through it with a difficulity level 49 it took me under 2 minutes and i got around 18,760 exp each time (levelups to 49 is 500k exp).