I concur with Hamburglar in that the SNES' RGB isn't as sharp as other systems like Genesis, SMS, PC-Engine, Saturn, etc. The SNES has a bit of blurring/trailing capacitance on the right side of high-contrast objects that the other systems don't have. (I can't speak for the SNES Jr.)
The S-Video on SNES is clear enough that RGB isn't absolutely justified. I don't have S-V shots but my page here does have some composite-RGB comparison shots:
http://www.chrismcovell.com/gotRGB/rgb_compare.html