I really liked this one where the backpack straps and panier attachments are on opposite sides of the bag, the conversion is quicker (just flip the top flap over) and it's more comfortable as a backpack than others I've tried. It got me through 4 years of college (overloaded with textbooks biking ~8 mi each way) but definitely started to show some wear, probably not quite as durable as an ortlieb but a great bag for $99.

https://banjobrothers.com/collections/backpack-panniers-banjobrothers/products/backpack-pannier-banjo-brothers