The toughest bags I have are old. Really old. But they've lasted and still seem to have almost infinite life left in them.

A small duffle, maybe 10" diameter by 14" long, made by Kelty. At least 25 years old.

A "Klettersack", made by Wilderness Experience, also more than a quarter century old.

The only new bag I have that feels as solid is a Deuter Futura 32. Actually this thing is just about bomb-proof. I guess I'd have to say it betters the bags I mentioned above. The bags above are extremely basic. In contrast, the Deuter is pretty high-end technical. It's maybe a bit large for warm weather day hikes, but perfect for warm weather overnighters or cold weather day hikes. But the thing is so dang comfortable that I end up taking it on most warm day hikes anyway. The Air Comfort system is wonderful. There are some detailed reviews of this bag at:

http://www.backpackgeartest.org/reviews/...%20Futura%2032/