Thus is just a quick little test I did between these two lenses. I had the Canon EF 28mm f/1.8 first and was happy with it. Then I got the 35mm L-series lens after and straight away I wasn't sure how I felt about it. Those feelings led me to this simple test and it was honestly enough for me to come to the conclusion that the price difference of the 35L to the 28mm was not worth it.
Of course 28 and 35mm are different focal lengths and 1.4 lets in more light, but I found the 28 to sharper, pretty close in terms of bokeh and close enough in focal length to satisfy my needs. I should also mention I shoot a lot of 50mm and I found 35mm to be just a little to close to 50mm for me to ever want to use the 35.
This simple test clearly will not satisfy everyone. I was honestly only doing it for myself as I found my 35L photos to be pretty close to my 28mm photos and in the end I decided the 28mm was better for me, but that's not to say you will come to the same conclusion. Use whatever lens suits you best, for me it was 28mm.
Thanks for stopping by, Rob