I had a Pioneer 757Ai and after recently upgrading my plasma to a 50"" hd one found that on certain dvds especialy during dark periods that there was a lot of smearing. So I borrowed a friends Denon with hdmi and upscaling and tried the same disk and no smearing. I put the smearing down to the fact that the Pioneer had no digital link to the screen as well as the upscaling process being done by the screen.
The result was I ended up upgrading the 757Ai to a Denon DVD 3930 which I got for £550 ex-demo and the differnce is breath-taking. I have it wired up via aQED hdmi and set to 720p and all traces of smearing have vanished, but more importantly the whole picture has inproved from colour delivery to delivery of great solid blacks. Cd palyback is also better than that of the Pioneer. And as easy as pie to make multi-region.
I personaly am not ready to comit to either HD format just yet, and from what I have seen of any HD player, none of them do any where near as good a job as my Denon with dvd or cd.