The trick here is to ensure that your TV is big enough to fill your line of vision, but small enough to be sharp and clear. Remember, if you intend to only watch standard-definition sources, the bigger the screen gets, the worse the image will look.
The ideal screen size can be calculated by multiplying the distance that you intend to sit away from it by 0.535 and then rounding this up to the nearest size.
So, if you sit 80in away from your TV, the ideal size is 42-inch (80 x 0.535= 42.8).