MARIO AND LUIGI
Very old Mario and Luigi
This image of Mario and Luigi was more common on the box consoles (the really cheap ones) so thats why the graphics are kinda bad. Also, the graphics then were generally poor thus giving the picture a more square and unhuman like look to it.
Old Mario and Luigi
The graphics and the general look of this image has drastically improved from the last one. You can actually tell Mario and Luigi apart now :) These look like the characters of the Mario time game. I love that game :)
Modern Mario and Luigi
Mario and Luigi look very 3 dimensional here. These good graphics can be found on the more modern versions of Mario games, such as Nintendo Wii games, Nintendo DS games etc. I think that i prefer the second image of Mario and Luigi because although it's 2D, it gives a more subtle feel to the picture.