I have a Sony CRT RPTV 57" (KP-57WS520).
I have the Toshiba HD-A1 and I've tried a number of other SD upscaling players (Denon 3910, Sony 9100ES, Oppo, etc.).
While I'm very happy with the Toshiba for SD, I'm still not sure if I like upscaling better than just plain old 480p.
With upscaling, I no longer can see the dreaded horizontal scanlines that are sometimes visible.
However, with 480p, the image is a bit sharper and more defined.
The Avia resolution patterns do show very slightly more detail with upscaling. The tips of the white lines are more visible...where as they start to disappear at 480p component.
But, the sharpness pattern shows the text is very slightly blurred at 1080i upscaled (despite all inputs on my display being calibrated).
So, in essence, for me, each input has positives and negatives. Which is best? I'm not sure. It depends on what day you ask me.
