I spent a lot of time hunting and found the Timbuk2 Ace bag to be the perfect fit (and love it). It’s a rectangular backpack (so maybe a bit ugly to some). Backpack straps can be stored and the bag nicely turned 90 degrees for attaching to a luggageworks J-hook. Perfect amount of storage as well.
I’d buy it again and again.
https://www.timbuk2.com/ace-laptop-b...r-bag/354.html