since I have been active in the mentioned recent threads about the 35mm Canon LTM lenses..:
I have the 1.8/35, 2/35, 1.4/50, 1.5/50, 1.8/50 Serenar and black, 1.8/85, 1.9/85, 2/100, 3.5/100 silver and black versions and the 3.5/135
Collecting these Canon RF lenses has been a different experience than collecting Takumars which almost sure will come in good working order. Specially when buying a black 1.8/50 and 3.5/100 chances are that the lens will have a milky inner element that more or less strongly impacts IQ negatively and which often can't be repaired. I bought 3 of these lenses to have one that is just almost clean. Those that can be cleaned usually will need opening and cleaning again and again. But they need a shorter adapter for my mirrorless cams and generally are smaller and ..also handle quite well and that has made me collect and lately choose them over my Takumars. I also prefer the aperture ring at the front of the lens. ( early Takumars have that too )
Most lenses I have used too little yet to say much definite, here my trial:
The 1.4/50 has impressed me above all with colours, also good sharpness and contrast
The 1.8/85 and 2/100 are very good, impressive performers, sharp from wide open, contrasty. But I rarely use teles and if so prefer smaller and lighter ones. The 3.5/100 definitely would qualify, but because for long I have not had a good copy I rather have been using the very good M-Rokkor 4/90 and Pen-F 3.5/100. And then there is the issue that I usually focus wide open and that changing aperture on these Canon tele lenses offsets the focus. I don't like that, actually fixed my lenses so that they wouldn't do that, but it makes operation a bit 'less certain'. The 3.5/135 also is real fabulous though!
The Serenar 1.9/85 is very sharp from wide open too and has, let's say, very unusual bokeh. More often this may disturb but I like lenses with individual drawing and that can be used to it's advantage too. I am looking forward to that!
My Serenar 1.8/50 is clean and may outperform my black copies, but it's very heavy and therefore I rather have used the black which is ok, but more grabbed a lovely Topcor-S f2/5cm, a wonderful lens.
Best I know the 2 35mm and I had shared my view in the thread comparing the two. They are quite distinct, the f1.8 is unique and interesting, the f2 more conventional but in numbers sure outscoring the 1.8 and more universally useable.
The f1.5/50 is one of the lenses I have been looking forward most. It has not grabbed me as much as wished and I have not been using it all that much yet, well, I have too many lenses..but already it has given me a few images that I like and I shall use it more