Now I've gone MFT, I plan to eventually get a nice lens around the 15-20mm mark as my walk-around lens for travel and home videos.  In combination with the ETC mode on the GH5 that makes it a ~35mm lens and ~50mm equivalent lens - the two most flexible focal lengths. My criteria are: nice MF ring aperture control (manual aperture ring or electronic control from the camera are both fine) faster than 1.8 nice 3D rendering neutral or on the warmer / nicer /