The weak point on Ortliebs is the plastic rails the hooks attach to, which eventually deform. Arkel uses a metal rail. However, Ortlieb's fabric is more durable than Arkel's, especially the Classic line with the old PVC coated fabric.
I prefer pocketed panniers to single bucket panniers. Lack of any external compartments is inconvenient.
I like a couple of exterior mesh pockets to dry out wet gear during the day.