I've found that the best place to level up was Transverse Town. Starting out in the Third District, then heading to the Second, into the Gizmo shop, then the Hotel and out into the Alleyway. Go through the First District and back into the Third.

If you've been to Hollow Bastion the first time, then Defenders will be your best bet on getting munny. One circut through the Districts has usually yielded about 4000+ munny for me.