Check out a lot of different panniers, and then trust your judgment about which to buy. After you have inspected five or ten different brands and models, you will probably have a good idea of what is important to you. Choosing the right set of panniers requires a balance between capacity, easy of loading, ease of mounting, durability, waterproofness, and more. "Perfect" panniers do not exist. But it is not hard to find panniers that will serve their intended purpose.

I place a premium on durability and repairability. I resent paying good money for junk. A few years ago, I bought a pair of Cannondale panniers that fell apart after two or three seasons. They are beyond the point of repair. Meanwhile, the Cannondale panniers I bought in 1989, made of heavy Cordura nylon, have needed a few stitches and patches , but are still going strong in their 21st season of use!