USB+UPscaling is best done by non-DVD media players like WD TV (7K)
Philips DVD players have divx ultra certification and plays anything and everything. It also plays MKV aand MP4 like WD TV. But upscaling capability is limited.
LG DV388 comes close to philips in USB performance. I persume upscaling also is similar to philips and both falls short to WD TV.
Pioneer 420 has good upscaling capability but the USB playback is limited to divx SD (.avi files). It cannot play any form of HD as I read from reviews. Sound is also supposedly better than the philips&LG.
No idea about samsung though..
Choose WD TV or philips or pioneer depending on above.