The advantage to SMall World Vacations is that they WILL keep abreast of any codes or sales, etc. Booking through WDTC won't get you those, UNLESS you call persistently and keep asking.
I have done both, and have gotten good deals both ways. If you don't mind doing your own homework, making lots of phone calls to WDTC and being pushy about them finding you a better price, then I'd say go that way. It's good to check on this website and mousesavers.com for any special deals and codes and then call right away to apply them to your ressie.
If you're booking a Good Neighbor hotel, however, I'd deal directly with the hotel if I were you.