I've had mine for about a month now.
Stunning handset, the camera is phenominal, the apps available on Android are so wide reaching that you will almost certainly never need to buy anything. Cannot recommend it enough, the only flaw is the devices build quality. It's by no means shabby but a case is essentially for it.
I would advise against selling the iPhone 4, you will no doubt have apps that you have paid for on it. Once the sim card is out it can still function as an iPod touch. I still use my old iPhone 4 for Mapmyrun, the gps still functions even though the sim card is redundant.