Graphics quality per screen size is something of a misnomer. It all depends on viewing distance. As long as the screen occupies the same angle of vision screen size makes no odds. Sat at my computer my screen occupies maybe 20 degree of my field of view (horizontally). Stick my nose close and it's occupying a much larger area, and look more pixelated as each pixel is presented to a larger area of the retina in the eye. So a small screen up close looks worse than a big screen far away.
Knowing how far you'll sit from your TV you can pick one of suitable size, and then it's down to image quality more than screen size. Though many people might find a smaller screen of higher quality because they sit closer to it and the average Joe is ever so slightly short (near) sighted.