There’s a post on Slashdot linking to an article on Gamasutra about why you should consider developing using Android.
Native SDK: http://www.engadget.com/2009/06/25/android-1-5-gets-official-sdk-for-native-development/
Update (December 15th 2010): At the time, I was not sufficiently informed about specifics of development for either Android nor iPhone. Currently, I believe native development for iPhone is far easier and better done. Objective-C is quite similar to C. With iPhone, one does not have to get his hands dirty with Java, and sometimes it’s even possible not to touch Objective-C at all. I haven’t worked with Android, but their current SDK does not inspire me to create anything. If I were giving an advice today, and you had to make a choice, I’d say you should develop for iPhone, no matter what.