I've used Kelty cheapos from Campmor for the last few years and they've been fine. I've also owned Eagle Creek and they're definitely a bit sturdier but not really worth the extra bucks to me.

Just be sure to get something with really good, big zippers. That's the weak point when they're tossed off the top of a bus in Bolivia or a yak in Tibet or a baggage cart in LAX.

Since luggage allowances were lowered several years ago I'm using a smaller Kelty and a bag I bought for 6 bucks in Kathmandu several years ago. Both are holding up well.

With baggage weight allowances being what they are duffels make a lot of sense. If I'm going on a mountain trip it's so easy to get to 50 lbs. with a 2lb. duffel. I can't understand 12 lb. empty bags.

If I were buying a new duffel today. I'd buy a Gregory Long Haul. The company has a great reputation, looks like good material, light. A little pricey at $70 t0 $110, though. Available at mountaingear.com and others.