I've installed all 3 brands listed. I do believe the Pac Brake bags are a bit nicer, but I've never had a bag failure with any of them.
We've built lots of custom air systems to meet specific needs. The weak points of the systems are usually the push lock fittings, but if cut at a perfect 90 they last a long time.
I would never tie both bags to the same fill without a valve in line. if you keep them separate they help fight sway, if you T them together the air will transfer side to side and make it worse.
Lastly as far as brakets are concerned, i try to install the bags that go under the frame just for protection and minimized leverage against the brackets and bolts.