The MOLLE pack is horrible, mostly due to the frame. It absolutely will break at some point. I went through 4 frames in one year in the Marines, and I was in artillery. We never humped our packs, just stuck them in the truck.
ALICE, on the other hand, that's what we used in bootcamp. Those things are effin' durable. The external metal frame and double stitched webbing survive years of the harshest abuse that recruits, and drill instructors, can put them through. Not extremely comfortable for extended wear, but they can definitely take a beating.
If you can find one, the new ILBE packs that are in service now with the Marines are EXTREMELY comfortable, and pretty durable too. It's pretty much a civilian pack with digital cammie fabric. Only issue I had with that was the 200 straps that connected to nothing and seemed to serve no function. Duct tape fixes that, though.