I've never looked at either one, but I suspect it might depend on which one has the latest item - for you.
Is there some reason this is important to you? What does it matter?
Because, if one doesn't click on both, one will have to assume that they are interchangable, and they are not.
I seldom find any answers to my posts in "replies."
I find, lately, that all the new posts are coming up in "replies" rather than in "unread," where they should.
Other interpositions would really cause problems, this is rather benign as long as one mitigates by clicking both.