Which one fits you better? I dislike the look of the Merkel stock, but it does seem to fit me very well. I don't know much about the Chapuis but I have owned several Merkels, a Blaser, and one Heym (soon to be joined by a second Heym). The most outstanding so far for accuracy has been my Merkel in 9.3x74R. I drilled and tapped the rib and mounted a scope and i can reliably ring the 12" metal gong at 300 yards with both barrels. Sighted in 2" high at 100 yards, i simply aim at the top of the gong at 300 yards and hit it every time. On paper at 300 yards, the individual barrel groups print about 6" apart and are on the same horizontal plane. To mount a Trijicon RMR, one needs to purchase the Trijicon mount for custom rifles with a 14mm rib. Then one needs to find a good gun smith/machinist that can mill the correct 60 degree groove on eithe side if the rib and a blind locating hole on top of the rib. My Heym was already set up with the grooves and the blind locating hole right from the factory and the correct mount is the mount for custom rifles with an 11mm rib.

On the Chapuis, I do not know how wide the rib is. One can always drill and tap and mount a weaver rail for easy mounting of optics however this tends to make the Trijicon RMR sit just a bit too high and makes lightning fast handling and target aquisition a little slower because the sight does not naturally find a place between one's eye and the target without adjusting of one's cheek weld to find the red dot.

Back to your original question, my understanding is that Chapuis and Merkel are within kissing distance of each other from both a price and build quality perspective. I am absolutely convinced that the Merkel won't disappoint you wrt to a quality build and accuracy. The only criticism I have about Merkels is that my bore scope reveals some atrocious chamer reaming work that leaves smeared lands in the throat area. I've experienced no accuracy problems due to this to-date however.

Incidentally, my go to double is my 9.3x74R Merkel.

I dislike the Blasers and the more I learn about doubles, the more I dislike them.