I tried both. I borrow some Arkels once from a friend of mine for a 4-week trip in Canada and I own some Ortlieb back-roller, and some old bike-packer. Arkel are nicely made, but I don't like to have to cover the panniers every time it looks like it is going to rain and to put delicate stuff in plastic bags. For me, panniers should be waterproof. I don't care to have everything in the same pocket, so Ortlieb panniers are what works the best for me. And by the way, you can use side pockets on the bike-packers.