A question I'm often asked - what is your favourite 50mm lens? - is tough to answer. In terms of aesthetics, Voigtländer's 50mm 1,5 Nokton ASPH is hard to beat. And while its handling isn't great, it is also built damn well. Its colour, bokeh, and overall draw are ridiculously good. It retails for around 1000$ USD.
Canon's classic L-mount 50mm 1:1,4 is often called the Japanese Summilux. As well it should be- it has wonderful colour, similar coatings, and an optical makeup that's not far from Leica's classic. It also has great bokeh, though, like the Voightlander, pincushions here and there. It can be found online and in classic camera shops anywhere from 150$ to 400$. At either end it is worth it.
But my favourite fast 50mm lens Leica's classic, pre-ASPH Summilux, preferably in M rather than L mount. Pictured above is the L-mount version in the newer pre-ASPH barrel. After taking it to Disneyland on a Sony A7r I became a convert. I love its cooler colour, smooth, but characteristic bokeh, its fall off, and its total sharpness. It and the Voigtländer aren't that far apart, but where the Nokton pincushions, the Leica remains smooth. Because it is long out of production, and because a rising number of people prefer non-ASPH lenses, its price has skyrocketed. In 2014, it went for about 1600$. Now it can fetch as much as 4000$ at eBay.
If you find one in good repair under or around 2000$ run, jump, and swim for it. It will keep its value.