My absolute favorite is the Feldherr Storage Box FLSB150.
I have a Maxi Bag, but have the issue that because there's nothing rigid in it, trays can bend if the case isn't laid flat at all times. I've opened it and found that minis fell out of their spot and into an adjacent spot. I plan to put heavy cardboard in the front, back, and bottom, and hopefully that'll keep things rigid enough.