Ortlieb are the go to, waterproof, proven on many round the world trips, bit too much plastic in high stress areas and silly clips to lose for my taste.
I use crosso expert made in Poland, as waterproof as ortlieb if you get the pvc? ones, 2 big metal hooks at the top for over the rack, metal hook on a strap for the bottom fixing.
If you want old skool cool, go Carradice super C made out of canvas you’ll be handing them down for generations, Carradice also do excellent waterproof panniers as well, Upso their offshoot brand is worth a look if you want individual looks.
Altura are excellent if you’re on a budget.
To sum up
Crosso,
Carradice/Upso
Ortlieb,
Altura.