35mm: in case you can live with the speed, the CS 2.5 would be my first choice by far. excellent performance for a ridiculously low price in Leicaland.
The old canon 35 can be very fine performers, but their minimum focus distance is 1m, which is a deal breaker for me. I had a 35 1.5 and it was very sharp. flared easily though.
for the 50's, you are blessed with more options.
The canon 1.8 black would be my first choice. great performer, very low price.
second would be the canon 1.4, with the advantage of the speed. Only drwback I found lately is distortion.
then, prices clim a bit: nokton, hexanon, planar, a cron from the 70's etc...
Personally I would leave the fsu out. Too many chances to find yourself with a paperweight...
Good luck and welcome to RFF.