For example, if the answer was the 1.8, you would buy a 1.8 but there is always sample to sample variation. Magazines compare two specific lenses and one comes out on top; the next two samples may reverse the comparison. Buy one each, test them, then keep the better of the two. Tha way you know for sure you own the one that satisfies you.
Years ago I recall reading the pros would borrow a number of samples, test them, and only keep the best, or, they would request the factory to measure and select for them. Decentered elements during assembly can make a huge difference!
My own story: I once had two Contax Zeiss Planars, a 1.4 and a 1.7. Everyone raves about the 1.4. I tested both and the 1.7 was 10% better in lines resolved across the range, aperture to aperture.
Last edited by Fred Aspen; 02-02-2013 at 08:04 AM. Click to view previous post history.