I love duffle bags -- we have Lands End bags, and I like the way they have a kinda "square" C-shaped zipper top, which means you can see everything in the bag easily. What I don't like is that the sides don't stand up on their own.
I also like the BIG -- no, GIANT -- Vera Bradley bag, which is probably the size of a Lands End or LL Bean medium-sized duffle. It does stand up better on its own, and it has pockets inside /out.
As for larger luggage I LOVE the four-wheeled spinners -- I have only one, a carry-on size. You can roll them "flat" or tilt them like a two-wheeled suitcase. I personally have never had any problem with wheels popping off, but I don't check bags. Ever, never, nope. My suitcases are never out of my personal control.