Whatever you buy, I suggest getting something better than a bungee suspension. Hooks that are adjustable fore and aft are also priceless.

I've had these for about 8 years and they've been absolutely bombproof. Not waterproof, but it's only been a problem in pouring rain.

Amazon.com : Inertia Designs Cam Excursion Panniers-Black : Bike Panniers And Rack Trunks : Sports & Outdoors