You've asked 3 different questions:
1) Most Romantic (at WDW);
2) Most Romantic
DVC overall; and
3) Best for couple in their 20's.
I have 3 separate answers
1) "Romance" is very much in the eyes of the beholder. I can argue for each of the resorts at WDW as being most romantic. The reason I choose SSR at WDW is two-fold:
DTD is a great place to spend an evening (cirque de soleil; a movie; great dining options; and
the SSR spa is nice and a couples massage is a great way to spend some romantic time.
The resort itself is beautiful. Interestingly, SSR is not my favorite resort, but I chose it for a romantic getaway myself and I was very happy!
2) Now...add in the two non-WDW resorts and...I definitely have to give the nod to VB. It is simply beautiful and, although I am not a beach fan generally, it is a very romantic place overall.
3) The location of BWV, with proximity to BW and Epcot, would put it into top slot for people in early 20s. I would easily include BCV in here as well.