B&W 804 diamond or previous 803D?

The 803D is the better value.
The 804Diamond is worth thousands less as soon as you take it home.
The 803D is going to be worth exactly the same as you PAID for it months, maybe years from now
And I think the 803D will sound better.

As a second opinion Elizabeth is absolutely correct. You will be getting a better speaker for much less money with almost all of the "immediate" depreciation taken out of it already. It is not a trick question trust your instincts on this.

I also agree, and wanted to ask about your room size? If too small, maybe consider the 804D. Otherwise go for the 803D for sure. You will want a larger amp with it too.