I played around with comparing scaler chips yesterday, and this is how I would rank my equipment, scaling SD to HD, best to worst:
1) Oppo bdp-83 (DVDO)
2) Pioneer FPJ1 - JVC RS2 (Gennum VXP)
3) Onkyo TX-NR5007 (Reon HQV)
Onkyo is by far the worst. The most obvious way I can show this is text from DirecTV's OSD when sent at 480p. The text had all sorts of blotches around them, like nasty jpeg artifacts. I then tested the Oppo blu-ray player, first with "source direct", which sends 480i out for DVDs. The Onkyo still looked "bad", but the Pioneer FPJ1 looked better (also checked the OSD for DirectTV and looked far better on the FPJ1). I then changed the Oppo to upscale to 1080p. This looked better than both the Onkyo and the FPJ1 doing the scaling. However, there is some ringing.
I wish I had not sold my Lumagen HDP Pro. I did not realize at the time I could completely bypass the Onkyo's video processing. It had the best up-scaling performance, but when I was using it (without video processing bypass in the 5007) it would sense odd changes in the video signal and would try to re-sync the signal, which never happened before I owned the 5007. My best guess is that the 5007 was sending small blips of garbage once in a while which was confusing the HDP.