leveling maps would be glitterhelm insane for early game.
early mythical farming map would be bonus maps on insane hc campaign, or later campaign maps on nmhc preferably survival. Arcane library is a very op map in terms of difficulty and loot returns, same thing for moonbase.
early trans gear would be any bonus map on either insane hc or nmhc. Maps to try would be tinkerers lab, moonbase, arcane library, bucaneer bay, coastal bazaar, kings game. These maps are very simple and give great gear. If your farming campaign maps for armor make sure to bring in 4x of the same weapon type characters for less junk weapon drops. Also learning which maps drop what would be a great help such as arcane library dropping very good quality accesories on victory, certain map rewards for weapons with stats, certain map rewards for good dps weapons.
If you struggle with anything such as breaking in to nmhc make a jester to wheel or mana/purity bomber.