The best area to train

[DarkStar]

Actually, I'd suggest grinding up to level 50, because if you're where I think you are in the story, having your last Job skill and your full Job artifact set will be quite helpful.

Anyway, as for ways to level...
1.) Dungeons. I'd personally suggest Dzemael Darkhold, because Aurum Vale isn't actually very pleasant trying to grind. Also, you can get some nice equipment sets from DD.
2.) FATE grinding. I believe the best spot for this at your level is in Northern Thanalan. I'd recommend trying to get into a FATE party.
3.) Levequests. Not as good as the first two for pure EXP gain, but can be easily solo'd if you can't find a FATE party and you're getting frustrated with dungeons.
4.) Straight monster grinding. Worst EXP gain overall, but you can do it while waiting for a Dungeon queue or FATE to pop, or while heading between Levequest locations, so it's more like supplementary EXP.
5.) Hunting Log. If you haven't finished it already, do so, it'll give a nice little chunk of EXP to help you on your way.

That's about all I can think of right now. Happy hunting!

[Felis]

4.) Straight monster grinding. Worst EXP gain overall, but you can do it while waiting for a Dungeon queue or FATE to pop, or while heading between Levequest locations, so it's more like supplementary EXP.

You can also train your chocobo while doing it.

[ServerCollaps]

Actually, I'd suggest grinding up to level 50, because if you're where I think you are in the story, having your last Job skill and your full Job artifact set will be quite helpful.

Anyway, as for ways to level...
3.) Levequests. Not as good as the first two for pure EXP gain, but can be easily solo'd if you can't find a FATE party and you're getting frustrated with dungeons.

uhm, its the fastest possible way ingame to earn exp, you make like 20k exp/ minute, until you run out of leves
just do that single escort leve at mor dhona over and over, the escort takes 20 sec + some npc blabla = 1 min per leve and a 20k exp reward

[KefLO]

but the maximum one for me is only 10k, is there one giving 20k?