Back to Front -> Bedroom, bathroom, Galley, Lounge. Known as 'Standard Layout'. We looked at lots of boats before deciding this was best for us.
Chose this layout as the bedroom is at the back, so hidden and dark. The bathroom is to one side and not a walk through one, so we don't cut off part of the boat - it doesn't need to have the room anyway. The Galley is a U shaped one so people don't get in the way of the cook! The lounge fills up the rest of the boat and is bright and airy as the front doors have windows also. It originally had an L shaped dinette and built in sofa/bed but these were uncomfortable so took them both out and used the table as a breakfast bar near the kitchen with some bar stools and bought a proper sofa/bed - so much nicer!
I wouldn't change any more as it works perfectly for us. The boat is a Semi-trad stern, so have room at the back for guests etc - i have a cover that goes over it so i can still work on the engine etc in the rain!