are Best Ipod Interface?

I am getting mixed reviews on what is the best Ipod interface for my wife's rig. She has an Escalade with factory nav and I want to add an Ipod/Iphone interface so she can run the Ipod through the touchscreen and use the steering wheel controls. I know there are a few companies that make an interface that is essentially plug and play. Any thoughts on what is the best route?

Thanks in advance!!