What resolution do I want?
The standard middle of the pack HD TV will generally have an advertised resolution of 1080i, or 720p. Here is where the “i" or “p" tag is important to understand. Even though one has a higher number, it is an interlaced number. 720p shows more lines of resolution per refresh (720), where 1080i only shows 540 lines of resolution per refresh (two refreshes to make the whole picture).
Which is better? It depends on what you watch most. 1080i is showing you the full picture (assuming your source is 1080p), but it only shows you half the picture per refresh. So it takes two refreshes to display the full picture. Your eye can’t see this, but if the image on screen has fast movement (sports), you will see artifacts or blocky splotches. 720p will instead show the full image in a single refresh, but scaled down to its lower resolution. While some of the finer detail is lost, no artifacts or blocks will distort the image when there are fast moving objects on screen.
So both 1080i and 720p make compromises, what about 1080p? 1080p is the highest resolution that consumer TV’s offer and the highest resolution produced for consumer media, whether that be a Blu-Ray or an HD broadcast.
The reason why 1080p might not be the most viable option now is because it is more expensive than similarly sized 720p televisions, and aside from expensive Blu-Ray media, most TV is broadcast at a sub 1080p resolution, or is compressed so heavily that there is no noticeable advantage to owning a 1080p television. However, the quality of both television broadcasts and internet broadcasts continues to improve, making a 1080p television more and more relevant going forward.
Regardless of the media quality pumping into the television, most people agree that in screens under 50", there is no discernible difference between 1080p and 720p. Ergo, if buying a 42" television, you might be paying more for something you will never see.