I've been buying REI backpacks, they tend to grossly oversize the zippers, particularly on their travel backpacks. I have not had a zipper failure in, well since 2008 which was the last time I bought a backpack, because they (50 liter "large" travel backpack, and 18 liter "flash 18" backpack) haven't failed yet. I did have a clip failure on a timbuk2 messenger bag, but they gave me a replacement for free at one of their retail locations.