I am trying to make the exact same decision. The 3802 is available for great deals now as it is discontinued. The upgrades on the 3803 are not important to me. DD-EX replaces Denon's matrix decoding of the rear surround and video upconversion is added. Video upconversion is cool, but I don't really need it.
Well, I bought the 3802. It has many more features than the Pioneer (Multi-room Multi-Source) and lower THD while lacking none of the pioneer's features. I say go with the Denon, but if money is not an issue, then get the 3803. However, I got a brand new 3802 for $680 from Tweeters as opposed to the $1200 for a 3803.
Denon has always been superior to the Pioneers, Sonys, etc. The sound quality when listening to music is far better.