With 9 people going on vacation to Disney World it just depends what the dynamics are with everyone. If you want to stay all together then a rental home will probably be your best bet. You may have to have someone sleep on a sofa bed to keep costs down. This option will probably be better off site. Having a car when you are off site is usually a better way to go.
The perk of getting extra magic hours in the parks can be a real incentive to stay on site. It's only an incentive if you use it. Many do not like to get up early or stay up real late to take advantage of it.
A pincode deal has to be under the person who received it when making all the reservations. All the resort rooms you get must be under the pinholder's name and they become financially responsible for all those reservations.
We have stayed both off and on site and we really like the amenities for the money off site. Having an included breakfast has always been a good perk staying off site. You can get many places close by. Having your own car is the way to go if you are off site. There are hotels with shuttle service, but the schedules back and forth to the parks are pretty restrictive. Also, you get left off at a certain location like Epcot and then it's up to you to get to whatever other park you need to go to.
Most pincodes are a better deal or at least the same as what's offered to the general public. Sometimes, there are multiple offers available to the general public. Right now, the general public can choose from a resort discount or
free dining. If you stay at an expensive deluxe resort often times the room savings trumps free dining especially if there are one or two people to a room.
By going to Disney's website for reservations you can plug in dates and resorts and see what the price is without your pincode. You may have a link to do the same with your pincode. Then you can compare to see the difference. As others have stated pincodes will usually be a better deal than a general public offer and you get a jump on most on available rooms. There are only a limited amount of these offers available and getting a head start over any other offers can be beneficial.
If pincodes weren't a better offer one way or the other they wouldn't be so sought after.