I am usually able to make quick and definitive decisions on whether a particular photo should be in color or black and white. It is mostly an intuitive process, based on how subjectively appealing I find each version.
Every once in a while, however, I'm unable to make up my mind, finding both options equally interesting, even if for different reasons. This happened with the photo shown above. Here's the b&w version:
Pentax K10D + Zeiss Planar 50/1.4
I like them both. A lot! Maybe I tend to like the b&w a little bit better, but then I look at the leaves and stones underwater in the color version and I'm undecided again...