Both Merkel and Chapuis are good double rifles. Pick the one you like best. I like both but would prefer the Chapuis because I like it's lines better, especially the stock.
The 8x57IRS (JRS) is one of my favourites (have a DR and a Drilling) and would certainly recommend it highly. I don't like any rimless round in a DR bur 30R Blaser is a good choice if you handload.
Regards,
Jani