I had the 40mm hd limited and sold it (regret) to get the 35mm ltd (don't regret, should have kept both
). I now have a 40mm xs to compliment the 35 limited. Optical quality is just once aspect of why I choose a lens. If I were to choose a lens strictly based optical quality, I could just buy the best lens optically I could find( and get rid of the rest)...one lens solution. For me that is not reality.
The 35 limited is fantastic optically, but trying to capture a 2 year old running around is difficult with the 35 due to the long focus throw. The reason the 40mm works for me is: great optically, super fast focus and it is small and light. With the 40mm on my camera with a wrist strap, it is very easy to work with and quick. If i need faster aperture or small apeture, a 50mm 1.7.
Each person has to decide what is most important in a lens and try to find that perfect lens...which is why many of us have LBA. I would like to try every k mount lens made at least once...how many would that be?