IMO there's no question that the Summaron is a sharper, contrastier lens than the Elmar. )The coated Elmar, as would be expected, is better than the uncoated versions.)
The Summaron uses a collar to adjust the "click-stop" aperture settings which is more convenient than the Elmar's slide adjustment on the front of the lens. The collar also means that filters and hoods that clamp on the Summar won't impede adjusting the aperture setting.
I own two 35mm f/3.5 Summarons. One cost me $120 while the other came with a "set" and cost even less when the various parts are divided out. The Summaron is not difficult to clean and I've done both of mine.
Canon optics are certainly excellent and I'm sure Joe and others with experience using them are happy with the results. I have no experience with the WA Canon 35mm f/2.8 lens but would think it's a fine lens. I know my Summarons are excellent so can't justify buying the Canon to compare. Then again, shopping and comparing and making a choice is half of the fun, isn't it? 🙂
The image below was taken with my first Summaron.
Walker