I have spent way too much cash on Frickin fly boxes in my life trying to find the perfect one that fits all situations. There isn't one.

My favorite is a tiny little Wheatley my wife bought for me for Christmas several years ago and had inscribed. It goes with me everywhere and is small stream delight. After that my favorite box is a $15 Trout Unlimited double sided see thru box with foam slits that holds a ton of flies. It even floats. I should have bought everyone they had for sale.
HC