First play through you can get to 50 quickly and easily using: Main story, FATE's you walk by, side quests, class quests, hunting log, guild leves, regular leves, dungeons.
Second play through you've burned your main story so you're left with: Odd side quest you missed (not significant but I'll mention it), class quests, hunting log, FATE's, regular leves only (because guild leves are only worthwhile once for initial bonus and only to level 45), dungeons again but now randomly and rarely because they're not rolled into quests anymore.
Third play through you definitely don't have sh*t all in way of side quests so once you wear away everything your XP sources are as follows, in no particular order:
- Class quests
- Hunting logs
- Dungeons (again randomly and rarely as they don't factor in to quest progression)
That being said, here's some unsolicited advice from me to you. Leveling is boring. Is that bad? No. Just boring. Plenty of life is boring, it'll be ok. Levels 1 through 20 can be done a bit on your own from your class quests and then with FATEs exclusively. 20-50 rotate around in a group to the popular FATE camps. It's rather quick. I work for a living unlike some people I know and even given that, I managed 1-50 WHM (not my first class), in a few days (less than a week) of playing in the evenings only grinding FATEs. Remember to take a break for the sake of your sanity, not from the game because that'd be a waste of time, but from the FATEs, every 10 levels to catch up on your hunting log, your class quests, and to re-gear yourself.
Alternatives that you shouldn't waste your time on (if you want to get to 50 and fun doesn't take primacy over getting it done) when pursuing your second class on-wards: Dungeons - Don't bother. You'll get stuck in DF parties that are learning the mechanics of lower level dungeons. Is that bad? Again no, but it slows you down, the point here being 'get to 50'. Leves - Don't use them for this. They are extremely valuable if you intend to use them for gathering / crafting, even more so for gathering because that's well and truly boring and really slow since you don't get to trip into 50 like you can with 125k XP HQ turn ins on a crafting class or the very efficient 3x3 turn ins that aren't heavy consumers of leve allowances.
All this said, do you have to pursue FATEs like a robot to jam your way to 50? Of course not, pursue 50 in whatever way makes you happy. Will your path to happiness get you to 50 faster than hammering FATEs? No, it won't. There's nothing negative about any of this, you just have to be at peace with it if you choose not to pursue the FATE route that you won't be getting to 50 anytime soon. Edited, Oct 10th 2013 9:56am by Furiousnixon