I have an Arc'teryx Khard 30 liter that I got through their LEAF program. It is exceptionally pricey and at the time I bought it I had to wait for it to clear Canada to US customs. So it took about two weeks to get. I bought it before a deployment in 2013 and have taken it with me everywhere. Meaning: two trips since, at least a dozen "field" problems, and every range since. Other than a weathered exterior, it doesn't have so much as a busted stitch, fraying, loose seam, or any other sign of distress. I wish that I had bought one size up (the 45 liter). The 30 is great for most of my uses, but it won't fit an M4 with 10.5" barrel without disassembly. Other than that, I cannot recommend it enough.
I also have an old 5.11 rifle case that I don't really use anymore. Reason being is twofold: 1) it has these internal loops intended to keep your rifle from flopping around in the bag that popped their stitching within the first six months; 2) I bought a Pelican 1750 rifle case in 2014 and have never looked back. Again it is pricey, but with a foam interior, three carrying handles, wheels, latches, lock holes, and a hardened exterior, you really get what you pay for. I pack a rifle in this case for every road trip (it is slim enough to fit under the rear seat of my Silverado and in the trunk of my wife's Corolla). For competitions I can fit my 16" AR-15 along with my 18.5" Mossberg 930 SPX and 4.25" M&P and still have room for my chokes and a few spare mags. It absolutely rocks.
I had not thought of using tool bags, although if my Khard shits the bed, I will probably buy one just to try it out. It seems like a legit idea.