I will be the first person to admit that if you tell me one lens is sharper than another that I already have and hand it to me you will likely have to pry it from my cold dead hand. That said, I am enough of a realist to understand that I am not best served by ultimate sharpness when other considerations are factored into the equation.
One very important factor for me is size and weight. The heavier the camera/lens combination the less likely I am to carry it around all the time. My casual/street photography is usually done while commuting, hopping off the train and walking from one stop to the next. For these instances a small, light manual focus prime is my go to lens. In the instance of the photos I took in this post, it was my Pentax SMC 28mm f3.5 lens.
It was given to me by my father-in-law when I got my Pentax K200-D more than 8 years ago. It is not super fast aperture wise, but the colors are excellent, CA hard to provoke, and a joy to use due to how it feels in your hand and on your camera. All metal, perfectly weighted focus ring. It just looks good and handles good, is relatively small and lightweight. Oh and it is pretty darn sharp too. It may not outresolve my DA 16-85 but It is good enough and is much smaller!
I have a fair number of these vintage lenses and while they have their quirks they are unique and deliver just a slightly different look that makes me want to use them more!
These three shots were all stopped down to the f5.6-f11 range where I usually shoot it. In fairly strong morning light. They are all sharp enough for me.