Ortliebs have amazing waterproof qualities with no rain cover requirement. But they're typically one big bag with all the access through the top and you provide the organization.

Arkels provide lots of organization options in their various models, but need a rain cover for real water protection. I have some of the XM-40's (now XM-45) and love the top load, but with a big zipper down one edge for very convenient access, plus they're narrow at the bottom, so they can be more forward on a rack for better handling. My wife has an older version of the T-28 in a one-off blue color and still exclaims about how wonderful they are after more than 10 years.

Both brands are extremely well constructed.