As I have shipped well over 12.000 boxes in the past 20 + years, I can definitely state that they are all the same.....UPS / Fedex / DHL, etc.
2 problem areas:
1. the centers in which any box will be handled and thrown around multiple times, and
2. ultimately the driver itself....he who doesn't give a shti is working for all of these companies.....
Any insurance co-writers of these companies have the 200 lbs per square inch impact / policy for the shipping boxes. If there's damage, and the boxes are not rated at least 200 psi's then the insurance companies (which are a nightmare to deal with anyway...deny, deny, deny) will definitely walk away from their obligations..... All of our boxes are indeed rated the industry standard 200 psi, but you should check before hand whenever you ship anything.
Also, it is true that any box will lose rigidity after it's been shipped at least 1 time, so yes, all of the advice above about double boxing is a good one.....and even double boxed, make sure that the outer box is also rated at 200.....these MF's are really peculiar about this number.....
Good luck,
Klaus