I thought about offsite and then decided to spend the extra money to stay on property as this will likely be a once every 5 years vacation. I'm a bit untrusting of DVC rentals and didn't want to mess with vacation insurance.
I can only speak from personal experience as a renter, but I've never had any problem renting my points nor have my renters. I don't have the points now, but Dave's rentals is a huge site and I'm sure it works. If you are staying onsite, it is the best way to get the most bang for your buck in most instances.