The Panasonic 20mm f1.7 is known for its great optical quality. This lens is very sharp on the borders and on any other place between the borders. However, the sharpness at the borders is not as great as on the centre. But this lens is generally sharp at all apertures. The Olympus 17mm is not as good as this Panasonic lens especially in terms of optical performance. Optical defects such as chromatic aberration, vignetting and distortion are excellently controlled on this lens. However, vignetting is the main concern on this lens as it is not well controlled at f1.7. The other two optical defects (chromatic aberration and distortion) are excellently controlled.
Since this lens is very decent and compact, I am very certain that you love the Panasonic 20mm f1.7. The focus ring on this lens is very smooth and responsive. The fastness and accuracy of the autofocus on this lens is commendable. This lens works well with Micro Four Thirds camera.