Digital BW, The Print

LIke many things involving the digital darkroom, "best" is a relative term. There are any 
number of ways to desaturate an image. And starting with a raw file just adds to the options. 
You could desaturate in a raw converter like Adobe Camera Raw, Lightroom or Aperture. In 
CS2 Channel Mixer is probably the most intutive method, but you could use Calculations as 
well. A search on the web will turn up plenty of workflows that use duplicate image layers 
along with Hue/Saturation adjustment layers. And then there are some third party plugins 
that come with "film" presets. Any of these methods will give you more control than just 
using Image>Grayscale, which is just a preset channel mixer function.