I use crumpler kit, a wonder weenie and a fux delux. The wonder weenie is getting on for 6 years old and pretty battered, no longer competely waterproof but I put my shirt in a plastic bag anyway.
They can jiggle round until the strap slips off your shoulder if you're going off road energetically, even with the stabiliser strap done up well, fine if pooting. On road, perfect.
I have panniers, and due to the whole wind/drag nuisance I only use them if I'm going to be very heavily laden.
As I don't drive I've carted a fair amount of stuff about in/strapped onto the courier bags, several frames, pairs of wheels, A2 mounted and framed picture, even a full size upright dyson vacuum cleaner. When I went for 3 18litre tins of paint I did use the panniers mind 😉
I got one to start with becuase I found coventional backpacks highly irritating. I get a small spot in the small of my bag gets a bit clammy, but otherwise I find they're 99% better than normal rucksacs for commuting.