The green next to the dog's right eye in the color one draws the eye away from the dog because it is very bright. (might just be my ADD)
The catch light in the the dogls left eye in the black and white one seems too bright, and I tend to focus on it as a white dot rather than a catch light. (again might be the ADD)
I prefer the color version. I agree with Rick - the dog's color is an essential part of the picture. The difference between the color of the subject and everything else is a big part of the visual appeal of the shot.
The black and white isn't bad but I think it just needs more contrast. There's not enough differentiation between the subject and that busy bokeh.
I prefer the crop/composition on the BW one but would keep the colour. If anything, maybe desaturate the green in the background a touch to emphasize the subject.