TBH I find them all pretty much the same but some models have certain flaws that are not always consistant to the brand.
Things I look for:
Hardish pad, theres no point in a pad thats like a dish sponge.
Strong material, difficult to spot but I usually wear out the material either bu friction or some just seem to perish.
Poor stitching, thats anything from endura, who follow the spend your money on marketing rather than product model of business.
Straps that stay on your shoulders, I’ve had a couple of pairs that were just badly designed in this respect.
Good length in the leg, not too short etc.
Nice finish on the seams, no chunky hems etc.
Drop section I can get my John Thomas out of.
All of which makes it pretty hard to by them online 🙂 my faves are probably Pearl Izumi.