What image makes a better black and white version?

Often I see people post on social media that they "can't decide" which version they prefer.  Color or black and white.  I don't do a lot of black and white imagery, because I am really drawn to color, it makes me feel something.

Occasionally, there are images that even when they are shot well, the pose is good, it pulls some emotion out, there is something lacking.  These images could  be converted to black and white for more impact.  Or, should they?  

Believe it or not, there are images that simply look better in black and white.  It really has nothing to do with anything other than light, and a bit of color.

The best images you can consider converting to black and white are ones where the image is quite dark, with the majority of the light on the subject's skin.  

Here is an example:

The color image is ok.  It's not "wow".  I found the colors rather boring, but I knew the light was nice because it was focus'd right on the subject.  Once it was converted (using Black Dhalia from the Black and White Set), to me, it is now a much more impactful image.  The eye is drawn straight to the subject and the back ground becomes rather unnoticeable.