If you want to level up hella fast FATE's are the way to go
For me it's
Western Thanlaan - 1-7 north of the outpost (abuse the windmill area FATEs), 7-11 west of the outpost (the 5 FATEs cycle here on the bridge area before Horizon), 11-15 the water area between Horizon and Vesper bay (the 2 FATE's here)
Eastern Thanlaan - 15-20 before Highbridge (lots of chasing FATEs too spread out, but reachable ), 20-25 Highbridge area (very compact, Attack on HB I,II, II give ridiculous amount of XP)
South Shroud - 25-30 anything near the Quarrymill or other side of the Inn horizontally
Costa del Sol - 30-37 The whole Eastern Map, Cancer side, too much XP
Coerthas - 37-42 The grad daddy of them all, too many FATEs, not enough time to do all of them, Return by your team is key to getting good XP
Pro-Tip don't use Teleport >_<
Mor Dhona 42-45 Near the sanctuary and around it
North Thanlaan 45-50 *DAT Dark Devices *Bites Lip* EVERYTHING!
Go, Go, Gorgimera!