To be honest? Neither are a wise choice for the conditions you describe. If a rack trunk, pannier(s), or a Carradice won't work for you (for whatever reason), there are better choices in the backpack department.

I might have missed it, but that Osprey doesn't appear to have any kind of suspension to it. And that Cordura outer/truck tarp inner of the Chrome will ensure your cargo stays dry, but you'll be soaked...