Whether a 1080p set gives a better picture than a 720p set will depend on a host of variables. Viewing distance is obviously one of them. Quality of the source material is another. Consumer Reports is not a tech oriented site, but I've usually found their information accurate. I don't know if this link will work for non-subscribers:
TV resolution, buying advice, 720p, 1080i, 1080p
Is 1080p always the better choice?
Not necessarily. While a 1080p set has the potential to display finer detail than a 720p set, resolution alone doesn't determine picture quality. Other factors such as brightness, contrast, and color also come into play. Some of the top-rated TVs in our Ratings are 720p sets that have better picture quality than some 1080p models. Further, the effect of resolution depends in part on the size of the TV. You can best appreciate the finer detail of a 1080p screen on a 50-inch or larger TV, though you might see subtle improvements on a 40- to 47-inch screen, especially when viewed up close.