I bought a pair of Orange
Altura Night Vision panniers for my cyclocross commuter and only use one for commuting. It gets packed with spare clothing, bait box full of sarnies and a 1 litre stainless steel flask of coffee.
Gets used in all weathers and has never let in water, bright orange for daylight viz and plenty of reflective bits for night time shift work.
Even when packed full the bike never feels unbalanced.
The second pannier only gets used on holiday, usually to carry shopping between the supermarket and our campsites.