I used to be an Android user and loved my phone at the beginning. But, it crashed all the time (OS not completely stable yet) and the battery life was horrible. I know people with newer Android phones that say the same 2 problems still exist.
I am now an iPhone user and love it. As far as Siri vs Google voice recognition, you can pretty much get both on the iPhone. I don't have the 4S, just a 4. But I have the Google app, which allows me to talk whatever I want and it spits out a google response, on screen.
The one thing that I really miss from Android was the Google Navigation, which I thought was stellar with the voice nav, etc. I've found some apps on the iPhone (free) that replace that, but not as good. Other than that, so much happier with iPhone. And, recently ordered my wife the 4S.