I have the factory one and the nice thing about it is you don't even know its there. Aftermarket and you have to put it some where. I think it worth the extra to have dealer intalled option. Clean and nice!!!!
Adding on to what the above wrote, I think the ONLY disadvantage is that the display doesnt scroll the information sent from the satellite station. Kinda sucks, but I like the whole OEM integration. I guess its a trade off.