Cabela's Ripcord Duffels. I use one for all but my shortest trips, but Asher and I each packed one for this trip. I like these duffels because they hold an enormous amount of clothes and other gear, but unlike other bags I have owned, they have virtually weight of their own, and because they are fully flexible, they really don't take up any more space than whatever gear I tote on any given space. That's extra important for this trip because 3 1/2 weeks of travel and fishing calls for a lot of stuff and because we are traveling in my Ford Fiesta, which though roomy for its size is not exactly a giant car.
I've also owned one of these duffels for three years, and I've never gotten a tear in either or had any problem with zippers, despite extensive use.