My personal opinion... the argument of stairwell vs bedroom depends entirely on the layout of the house. In some floor plans, there may be almost equal advantages to both. Some places the stairs will be better, some the bedroom. Gathering family together in one room is a concern. If you are dealing with someone intent on doing you harm, you probably don't have a lot of time. Waking up takes a few seconds, then a few more to fully understand the gravity of what's happening. By the time you get a gun up, you may not have time to gather family. If it's just you (or you and wifey) and gathering family is not a concern, then the bedroom "line in the sand" may be your best bet.
Put a small night-lite on the bottom area of the stairs, and do not light up the top. That way, you can see down, but the intruder cannot see up as well.
This can be made to be a major advantage not to be easily dismissed. Proper use of lighting is important in a home defense scenario.