All of our rooms are difficult, so the differences are a matter of degree rather than kind.
We do not officially have ranking for the difficulty of our rooms. The main determinant of difficulty in our rooms is a willingness to ask for a hint when you are stuck. Groups that are willing to ask for help are much more likely to finish the rooms than those that are reluctant to do so.
Having said all that, The Bank is probably slightly more difficult than the other rooms and The Bunker is slightly easier, with Zodiac and The Prison somewhere in the middle.
To read more about our rooms, click here.