Your first suggestion, with the screen on the wall opposite the door leaves enough space for viewing, but it makes surround sound harder. Have you seen the seating distance guidelines from THX and SMPTE? This image makes for a nice summary - notice that the distances are given as ratios of image height.
Your 55" display will have a height somewhere in the 27 inch neighborhood, so the normal recommendation would be as close as about 5 feet from the screen. You'll feel weird about that, I'm sure. But with HD content, it's a great way to watch a movie.
I'd probably go with the end wall, placing the screen in front of the window. You'll want some good way to block the light from the window, but that orientation will feel more natural and make you put your seating away from the wall. We generally set up living spaces with seating along the walls, but that's a bad way to design a movie theater (a listening room). This gives you room to grow if/when you get a larger display (like front projection).