So you're aware, Ephinea has an extremely active Discord that you can dump questions into. You have better chances for quick replies.
No real issue with using forums though but I wanted to make you aware of the assistance you can get on the platform.
New Mop Up Operation #3 (NMU3) tends to be the target quest for exp should you have a carry. Another good option is to keep an eye on HBR. If the quests for a given month are manageable and enemy dense, you can grind them with a party. It doesn't take much score to get exp in Normal, Hard and Very Hard difficulties. Note that this only applies under Ultimate and on a char under level 100.
TTF gets old quick but it does help with exp if you're actually using it to hunt stuff, usually Red Ring. Levels really come fast when you actively hunt rather than haste for levels in a vacuum.
If all else fails, then NMU3 or TTF if you you don't have a FO to carry ep4. If you acquire Hell gear and have Rangers, they level easily in ep2 where Hell melts everything.