Manual focus macro lens, I'd suggest you to get the A*200/4 macro, A100/2.8 macro or A50/2.8 macro. It's alot easier to use an A lens (has an A setting on the aperture ring) when shooting macros.
Of course you can try the M100/4 and 50/4. As to which one is better, depends on what you plan to shoot at. For bugs, better choose a longer lens. For flowers, a 50mm lens would be enough. For product shots, I prefer 50mm, but I can live with a 100mm macro lens for production shots too.
There is no bad macor lens, all macro lenses are excellent. Just choose whatever focal length suits you the best. But I do suggest to at least get an A lens
Don't waste time with the M series as getting the right exposure can be a hit or miss affair. Stick with the PKA mount lenses and you get to shoot in every exposure mode (Av is very useful for macros).
Don't waste time with the M series as getting the right exposure can be a hit or miss affair. Stick with the PKA mount lenses and you get to shoot in every exposure mode (Av is very useful for macros).