Advice needed on merging two sites

I have two sites:

1. 12 year old site, hundreds of articles, DR15. Not a good domain name.
2. 3 year old site, hundreds of articles, DR27. Better domain name.

My plan is to merge them together (both in the same niche) and combine the content.

The issue is: I prefer the newer site's name, but I'm concerned about merging a much older (potentially more valuable) site into a newer site just to keep the better name.

Plus if I list the site for sale later on, I'll be listing a 3 year old website instead of a 12 year old website, which might devalue it in the eyes of a buyer.

Is there an ideal strategy here? Should I merge into the older site instead?

Does it matter either way for SEO or no difference?