I had the 27mm, great little street lens but the focal length just left me wanting. It's neither wide or long enough, it's just shy on each end. I'm much happier with the 35mm 1.4, which is neat and light enough for similar purposes but also better for portraits and artsy fartsy shots
I considered the 18mm too, but I have read some iffy reviews on it. Another lens I would like to try is the Samyang 12mm, which seems to get nothing but praise, and I don't mind MF. 3/4 of my current lenses are MF. 58mm, 135mm and 200mm. The 35 1.4 is my only AF lens right now, not sure 'exactly' what I would like besides.