Which Speaker should I buy?

Because of the size of your room and the wattage you are using I would get the largest most efficient speakers you can afford..personally I would prefer Bookshelf speakers or floor standing speakers to in wall units due to flexibility... in wall speakers once placed there is not too much you can do to tweak them...bookshelf speakers can be towed in towed out moved a couple of inches to the right or left...you would be surprised what just a little movement like that will have on the quality of the sound they produce...also they can be upgraded at a later date...