Patagonia: With Ventura-based Patagonia, you get what you pay for. What you pay is a lot. What you get is exactly what you want. Patagonia’s gear and clothing looks great, it works perfectly, and it is manufactured as ethically and sustainably as reasonably possible. I do not yet own a Patagonia duffel bag. But I do own a broad cross-section Patagonia clothing and gear, all of which may very well last me forever.
Glaser Designs: San Francisco-based Glaser makes absolutely beautiful duffel bags to order for "executive travelers," which I think means wealthy professionals who spend a lot of time on planes.
Mountain Hardwear: Richmond-based Mountain Hardware has been my go-to supplier for camping-and-backpacking clothing and gear for more than a decade. They also make duffel bags, which probably are of high quality, and which look nice, in an a-backpacking-company-made-this sort of way.
North Face: Alameda-based North Face makes pretty much everything an outdoors-enthusiast could want, including duffel bags. Judging by everything I’ve bought from North Face so far, their duffels probably are very well made.
Olivers Apparel: Los Angeles-based Olivers makes exercise and streetwear clothes for runners and gym-goers. Their offerings include duffel bags.