Ortlieb is widely regarded as the best brand of bike bags in the world. Every single Ortlieb bag is handmade in Germany and guaranteed completely waterproof and defect free for 5 years.
Ortlieb's labor intensive. high frequency seam welding method is superior to other products on the market whose seams are glued or sewn and Ortlieb's adjustable QL2.1 pannier attachment system is the best design on the market.
They are not inexpensive, but if you need bags that you can rely on, you will not be disappointed.