DVC has four resorts right now on Disney property, with two more planned in the next few years. If you're buying through Disney, only Beach Club Villas is available for purchase right now. However, you will find resales available through the Timeshare Store (linked at the top of this board) or atimeshare.com. There you will find older properties like Old Key West, Boardwalk Villas and the Villas at Wilderness Lodge.
To answer which is most popular is like asking someone which of their kids they like best. They're all fantastic but everyone has different things they like about each. Old Key West is on a golf course, with several different buildings made up of many units in each. It's a bit more spread out and away from the hussle and bussle. Boardwalk and Beach Club are in a more active area and within walking distance to MGM and Epcot. They are traditional hotel style buildings, as is Villas at Wilderness Lodge. The VWL is much like the main lodge - very tranquil and woodsy. It is very close to the Magic Kingdom (by boat or bus) but is also off on its own a bit with a woods/lake setting and very relaxing. Again, it just depends what atmosphere you like. You may want to visit
www.disneyvacationclub.com as they have detailed descriptions. floor plans and photos of all the properties.
AND don't forget you can use your points to stay at ANY of these fabulous places! So don't feel like you have to lock yourself into just one! Where your ownership comes in is you'll have the opportunity to book 11 months ahead of your trip at your home, but just 7 months at other DVC resorts. So if you often go at busy times or during school vacations, this may make a difference.
Finally, dues. They are based on your points and vary from resort to resort. I believe they range from about $3.25 to $3.75 per point (please correct me if I'm wrong, fellow DISers) and are paid annually in January. You can arrange to pay them month by month if you do a direct debit from your checking or savings account.
I hope that helps - if you have any other questions, just post!