lens choice: 20mm f1.7 or 25mm f1.4. ?

A site like lenstip clearly shows the difference in optical performance between these two, with the 25 clearly ahead, particularly on edge performance - slightly greater subject isolation can be achieved with the 25 because of its slightly more open maximum aperture and its longer focal length. In my experience its a beautiful lens to use, but it does leave a sizeable hole in the wallet!