One of the best ways is to do the RAW conversion in color, then use the Channel Mixer in PS (with the checkbox labeled something like"gray scale" or "monochrome" checked) to get the best mix of channels. A simple "desaturate" doesn't give you any control over the mix of channels to use, but the Channel Mixer does. For example, you can choose the channel (R, G or with the least noise, or the most contrast, or whatever other good effect you're most looking for, and use more of that channel in the conversion to B&W. You might even just want to use one channel and ditch the other two.
Lisa