I'm surprised by talk that the Nikon 50g is better than any Canon 50mm. Nikkor 50mm AF lenses have bad bokeh. Period. I really don't care much if (IF) a lens is 2% sharper than another if all the background bits are doubled and nervous.
I've had the Canon 50/1.4 for a long time. It's really good. If you get a good copy, it's sharp from 1.7 and smaller. I once had a Summicron-R 50mm and thought the Canon was as good or better from F2 through 4 or 5.6 (as far as i tested), but the Canon has a 'bonus' 1.4 and 1.7. It's not even bad at 1.4. It just has a bit of halation if you have white/bright areas in the image. Even then, it's not always bad. Bokeh is very good, although not as good as the newer 50L and Sigma 50/1.4.
I had the Sigma 50/1.4 for a little while. I liked it. Build quality is very nice. Focus is quick (enough for me). Bokeh is phenomenal. But, it seems to require a digital body with an AF micro-adjustment feature. Worked nicely on my 5DMkII. Didn't work (three samples) with the original 5D. I tried a Nikon-mounted version on a film camera (Nikon F6) and got horrible results, despite Sigma's claim that the 'focus calibration issue' is only an issue with digital sensors. Maybe i just had a bad sample again?
I had a Canon 50L, again for a short while - after the Sigma. Again, build is very nice. Both the Sigma and Canon are large, solid, heavy lenses. Again, though, i don't recommend the 50L unless you have a dSLR with focus calibration. Not sure how it would have fared on a film body. I have an EOS3 but never used it on that camera before i had to sell it. I'll probably buy another soon. I do think the Sigma's bokeh was better, though. Sharpness-wise, my Canon 50/1.4 was better than both the Sigma and 50L. The Sigma and 50L probably were tied for second.
I've had a 35L for about five years. I, embarrassingly, don't use it much at all. But, every time i pick it up and shoot it at home, i'm impressed. And, whenever i get a new lens, i compare it to the 35L. It's just a great lens. Sharp from 1.4 and with great bokeh.
I have the 85L. It's just the best 85 i've ever used, including the Summilux-R 80 and Contax-N 85/1.4. It's not quick-focusing, but it's quick enough to shoot what i shoot - people.
I would have switched to Nikon long ago if Nikon had such fantastic primes. I love Nikon camera body design, and also the fact that even the old SOLID film camera bodies use the same lens mount as the current digitals. I have an FE2 and F6, and once had F100s, an F80, and an F4. But, i only have an old manual focus 50mm Series-E lens to use on the F6.... I only shoot primes at the moment, and none of the (currently produced) Nikkors are better than the Canons. Sad, and odd, since the old manual 50s and 35s give such lovely results.
Get the Canon lenses. Don't bother comparing them to RF lenses. They're good enough to stand on their own merits. And with AF, and the ability to shoot wide open without worrying about missing focus because you've recomposed after using the center RF patch, plus better high ISO performance, cinematic video potential.....