I need to develop an app where several ipads communicate to a single main iPad. Would this be done using Bonjour or Game Kit? I looked at Bluetooth but that seems like a 1 to 1 communication. I have never messed with either of these API's
You could use Bonjour to do this -- but remember that Bonjour is only a framework to advertise services and doesn't do any of the actual connection itself.
For Bonjour, you need to create an NSNetServicesBrowser to scan the network (which can use Bluetooth -- or WiFi) and publish an NTNetService with the port for the other iPads to connect to (this could be the "master" iPad itself).
Then you would need to run a server on the "master" iPad (that is advertising the service) and then have some sockets code to handle all of that. (For which I recommend AsyncSocket (http://code.google.com/p/cocoaasyncsocket/).
Let me know if this is something you would be interested in doing, and I would be able to provide some code snippets as a starting point...