Gaffgarion for sure since its free limit break

Mont for sure, easy to LB and get to level 99. Great tank for pretty much any situation

Gaffgarion because you can LB to max in less than 2-3 days even if your slow to grind. Also great DPS character

Also I would say Mediena if you focus on her and slowly get her to max but maybe for right now I would recommend another MR or lesser unit just to have a character to level higher than 40

Thank you!

Farm gaffgarion shard for starters, then you can focus either on Mediena (IMO)

Unlock:
Fina: Cheer lvl 16. Farm for JP till you get her to that point. Then you can Faith raise any caster.

Short farm with Gaff and Mont for LB and solid damage.

Mediena Should be your first focus for long term PVE clears.

If you picked up Etre you can easily lvl her and ele chain with Mont for some mission clears. Rock throw and pummel.

Shard farm Engl.

Engelbert for sure best tank in game.
Mediena very good for story quests and multiplayer cause she can attack multiple targets at once attack.Leave Gilga for a while.
Gaffgarion free dark elemental easy to max LB.So yes focus on him.