we had a similar dilemma a while ago. We just put a whb in one room, for an au pair. It really depends how you think its going to go. If you are thinking au pair then the extra shower room is really handy, and if times are hard and you want to let a room, en suite is always better. If you have lots of stuff, it is not a hardship for family members to walk down a flight of stairs, but I warn you that teenagers spend a long time in the shower. They seem to stand there for 20 mins every morning to wake up. If you will have a few teenagers at the same time I would be generous with the provision of showers!! It is the older generation that need toilets on the same floor!