Which type of Walnut is better for furniture?

I don't know but let me tell you a story - being raised in Canada we had a walnut dining room table that - for years - had this large milk stain that could not be removed no matter what my mother did. One day she called into a helpful home hints radio show to find out if they had a solution. She was told to rub crushed walnuts on the stain and, sure enough, the stain vanished :).

Possibly the colder clime for strength.

They're both strong woods to begin with, whichever one has a grain pattern you like better.