The brand has the word and in it like Frank & Oak. I feel it's easier and better to have a shorter domain.
It's usually better to go with the shorter version if possible, for the sake of making it easy for people to type in. However, if it's a branding issue then the longer one. If people know you as "frank and oak" then that's better to go with frankandoak.com verses frankoak.com. If the second redirects to the first, you win no matter what.