Best legacy 50 f1.4 prime

I was thinking of the Canon FDn 50 f/1.4 as one good deal for ~80€ + adapter but then I heard of the Rokkor 50 f/1.4 as "one of the best 50mm ever made" and find it for ~50-70€ on eBay...

Now I want to ask only two questions:

When I am going to buy only one 50 mm prime, for which one should I go (max. 150€)? First I have seen some Olympus 1.8, then the Canon FDn 1.4 and now the Rokkor... every lens for between 50€ and 100€!

Is the SEL 50F18 in terms of picture quality anyhow comparable?