Both Jake and Finn start out at the same level, same experience range, but depending on who gets the finishing blow on big battles, there will be a bit of a discrepancy in their experience values by the end of the game. If you play through the game and focus on fighting everything directly in your way while solving all of the side quests, you should be eight if not nine by the end-game moment; from there, just focus on running through the Fire Kingdom gauntlet by starting with Cinnamon Bun, run left and up with the Trigger Action, and take down everything in your path as you go around in a clockwise/counterclockwise (depending on how you read the map) fashion.
Finn will probably be the third, if it's anything like my playthrough, as Finn had a lot more finishing blows than Jake did by the end of the game. This is probably going to be the longest of the trophies because of the values in experience not changing much by this point.