Ok. First a disclaimer: I am a senior systems engineer at Nokia.
My wife has an iPhone (recently got the latest iPhone 5 to upgrade from her previous 3g). I have an Android (actually 2 - Google Nexus Ones - personal phones), a Nokia Lumia 900 (work phone), and a Nokia C3-00 Series 40 phone (work phone for testing purposes). All of these are great phones, and using the Nokia Lumia daily has been generally a pleasure. It is reliable, responsive, and has some really good applications. As good as Google maps may be, they are still getting caught up with Nokia's technology (purchased when they bought Navteq a couple of years ago). Both Google Maps and Nokia Maps (with turn-by-turn driving/gps capability) are available on the iPhone.
The Lumia 920 is a major step up from the 900 I have. Nokia has the best cameras on any phones, and the 920 is no exception.
Android S3 is the best if you use it for multiple purposes includeing entertainment. there are lots of apps for android out there you can convert your phone into almost anything. go to play.google.com and you can see them. Nokia is doesn't have as much as good apps like that (as far as I know). iphone is ridiculously expensive and even if they were the same price, s3's hardware performance is better.
So if you use the phone just for calling and stuff mostly go for a Nokia other wise S3 (or iphone ) . go for an S3.