>>3472116First of all, it depends on what you want from the lens. Between all the 50mm lenses that have ever been made, and all the 50mm LTM lenses you can use with an adapter, there's a lot to choose from. A couple considerations to narrow it down: will it be used on film or digital? Do you want modern, flat, ultra-sharp images, or are you looking for something else?
If you want to use it on digital, seriously consider sticking to more modern lenses. Definitely go with something multicoated, and if you're very concerned about sharpness then you need to stick to very recent lenses. If it's for film, that's less important. If you're shooting mainly black and white film, consider some older lenses, including LTM.
As for some general recommendations, the Voigtlander 50s are probably the best value for the money. All their 50s are good, none are amazing. Some have more modern designs and coatings, some less so. LTM vs M-mount doesn't matter. The adapters are cheap and effective. If you don't mind going a little wider, the 40mm M-Rokkor is probably the best value you can get for an M-mount normal lens and outclass the Voigtlanders by a decent margin. The Zeiss planar very nice for what it is. It's made by Voigtlander for Zeiss using a classic optical formula with modern coatings, to slightly higher standards that Voigtlander-branded lenses. Don't expect it to perform like a modern lens though. The best value for a fully modern 50mm suitable for digital is probably a used Leica Summarit 50mm f/2.5 (or f/2.4 version: same lens, slightly different configuration, slightly more expensive). Rendering is similar to a summicron, but much cheaper than the latest 'cron, and a bit more character since it's not an APO lens.
