Upscaling in a DVD player properly consists of two processes, de-interlacing, and scaling per se.
De-interlacing is the more difficult of the two processes and deficiencies are often not noticed until after you buy the player and bring it home.
A DVD player that does upscaling to HDTV format but which has not so good de-interlacing is likely to give a poorer picture than a player that has good de-interlacing but no upscaling, letting the TV do the upscaling.
Do a Google search for Stacy Spears Shootout Secrets and check out some of the DVD player reviews there.
Video hints:
http://members.aol.com/ajaynejr/viddoubl.htm