Like others, have tried a variety of packs - Thinktank, Midshift, Fstop, Kata. Totally prefer the F-stops. There is just something well-thought out about their bags - they are comfortable and stay close to the body. I have two about the same size - an older Loka and a newer Lotus. The Lotus is lighter, the Loka a bit better built with more features. These are preferred to all other bags.
For simpler use, there is a small innocuous Tenba - one MF camera goes in a well padded bottom pocket, and then an extra lens up above. Works for walking around.
All the other bags are in-between in sizes, and once you start adding up the MF gear (its not so light) then fit and comfort become an issue. The F-stops are the best for walking several miles. The others might be OK for a short jaunt here or there, but largely occupy the "to be sold someday" corner.