I have been weighing up between the EF 20mm f2.8 and the EF 17-40mm f4L.
For EF 20mm: Better vignetting, distortion and CA than 17-40.
Sharpness seems about the same on good samples.
Against EF 20mm: Looks like it has more process variation than the zoom, don’t want to get a lemon. Not much difference in weight.
I had more or less settled on the zoom despite normally going for primes but I worry about the distortion as fixing it in PS seems problematic for fine detail. (see parallel post PS Barrel Distortion Thread
Anyone using the 17-40 on 1.6X crop and full frame care to comment on how noticeable the distortion is please.