Which is the best DVD upscaler? In your opinon.

Do you mean just a scaling device itself or a player? If a player, then the Toshiba A2 or Oppo.

I'd suggest the Oppo.

The player! Are those 2 better than the Denon 1930?

I believe the Oppo could be comparable to the Denon, for about 1/3 the cost. I don't know if you are counting options such as region free, upconverting hacks and SACD.

The A2 is a different animal, a HD player that does upconverting will. If you want to enter the HD format competition, this may be the way to go. Plus I think it is cheaper then the Denon as well.