I own a Chapuis and like it a lot, I've played with a few Merkel's and prefer the Chapuis, that's why I currently still own mine.
I like the suggestion of checking both out and buying the one that suits you best. Fit and handling of a double is paramount. After all this is one of its main advantages over other types of firearms.

I think price should be a secondary consideration ( assuming you're paying market value for each ). Either way, you're going to pay many thousands for a fair double, $1-$2K variation either way is irrelevant in the long run. My opinion anyway.