I change my mind about this often, I enjoyed the Australian Open though, looked very clear on the box. For some reason the US Open is the worst viewing, as if the camera doesn't zoom in enough at least on Ashe Stadium. So I'd put Australian Open ahead of US in terms of viewing.
Wimbledon and Roland Garros I'd have to watch again to decide on, since its been a while since seeing them last year. From what I remember of last year I'd expect it to be like this:
2. Australian Open
3. French Open
4. US Open
Australian Open maybe with the best camera-work but Wimbledon beats it because the grass is so darn tasty looking.
1. AO [Rod Laver Arena was designed with the cameras in mind, esp new blue court is great].
2. Wimby [as mentioned by theRafa~ grass is "darn tasty looking", though not sure about the new roof].
3. FO [PH stadium is a magnifique venue, though if the sun is bright its hard to see the ball].
4. USO [Arthur Ashe stadium is almost like a baseball arena, too big for tennis].