Obvious answer is Summilux 50 1.4 ASPH, but I don’t have this money, yet…
I was able to find locally, not expensive Summicron 50 f2 Rigid in user condition. It is big and heavy lens. Picture here is taken with this lens at f2. M3 ELC camera on the picture is with another lens which I shimmed for Leica. Old soviet Industar-22 50 3.5 lens. This is how it performs on M-E wide open:
Not so bad for tiny and light 19$ lens.
But I still need faster 50mm lens for indoors family pictures. I have tried another Soviet lens I have, which is Jupiter-3 50 1.5. It is fine lens for film M Leicas, but on M-E wide open it is “glowing” and I’m not big fan of it for indoors portraits.