I've noticed that upscaling players don't do as nice a job w/ 480p as they do with 720p or 1080i. I have a Yamaha 2500, Denon 2200 and Harmon Kardon DVD25 that don't upscale, but they have a nicer picture at 480p than my OPPO 970HD or Toshiba A2 when all are set at 480p, but when comparing 1080i from the OPPO or Toshiba, they have nicer pictures than the others. Different chipsets in almost all the players, the Yamaha does the best PAL to NTSC conversion with the Genesis chip, the OPPO has the best seamless layer break with it's Renasis chip, the Toshiba has the nicest picture overall, but the OPPO is close, and it has a slightly better audio transport IMO.
Hi-Def Format Neutral
Samsung BD-1400, PS3 40GB
Toshiba HD-A2, HD-XA2 & XBox 360 HD DVD