Choose the one you like, not what someone else likes and enjoy!
 

I agee "Pre war Merkel's quality is akin to best Birmingham guns." I have several post war Merkels. Well made and lock up is excellent.
The single trigger/double triggers is sometimes an issue with functioning on any make. My Parker Repo single trigger always worked as expected.
Choose the one you like, not what someone else likes and enjoy!

I have a pre-WW1 hammer gun and a Sauer 3000Lux drilling. All overbuilt and very very tight as the day they left the factory. The German national motto is “If it is worth doing, it is worth overdoing!” They mean it

The hammer gun is a Merkel sxs.

I've owned many of both and love both guns. As for quality of construction i'd have to go with the Merkel. Built like a tank and will virtually last forever if taken care of. I've had both single and double trigger Merkels and never had any trouble with either. I agree about the wood not being as pretty on most Merkels but I've had some that were what I call "oh my god" wood. The Parker Repros most commonly used California Claro which isn't as tough as the wood Merkel uses and they weren't as careful with grain layout through the wrist ares where it is so important. Thus you do get some of the Parkers that break in the wrist area. Either gun will last as long as you want it to if taken care of.