Speakers with no rear wall, better or worse sound?

I have been in a debate about speaker placement. I was proposing that having speakers in the middle of a long space (~30 foot long room) would be preferred over having speakers about 3 to 4 feet from a wall behind the speakers. I would think that having little to no wall reflections of sound from behind the speaker would be preferable. The wall behind the speakers is currently about 14 feet back. Another opinion suggested that we should build a wall 4 feet behind the speakers to get the best sound. I was thinking that the reflected sound from this new sound would mix with the speakers' direct sound and erode the quality. Other views? We were considering some renovations and I do not want to go through a significant change to our home and erode sound quality.