I think the thing to consider is what is most practical to your users. I want to be able to login at yourdomain.com I don't want to remember that I have to login at app.yourdomain.com. I think ultimately providing the simplest path for your users to sign up and log in with is what you should do.

What might make the most sense is putting your marketing site in a sub-directory like /tour or something and then get another domain just for marketing that redirects you to the /tour marketing page.