I have been using an Ortlieb Vario (latest model) every weekday for nearly a year and it has been fantastic. I'm an industrial designer who has designed many bags. This is hard to beat. I'm typically not a fan of the overly engineered plastic/advanced manufacturing methods, but it is extremely effective in this context. The most important elements are all a 9/10 or 10/10, being:
-Minimal friction to convert from pannier to backpack. Takes me 3-5 seconds. If this isn't easy, you will not be encouraged to use the feature.
- Straps/back of the bag/anything that touches clothing is fully protected from road grime.
- The backpack actually functions well as a backpack. Mine is VERY heavy (I carry a full mobile office in it) and it handles the weight VERY comfortably.
Retail price is very expensive but I got mine new off eBay for a considerable discount. Very minimal organization, but excellent size, especially considering the option to expand with the roll top. As with all ortlieb products, I can bike in a downpour and have zero concern for my electronics.