I have a 4S and an Android phone (the Droid X2). I use the droid as a beater phone for going to the beach. I just switched over to the Droid yesterday and immediately noticed the sad state of the Android apps. Most, but not all, iOS apps are available on Android, but:
All the Android apps I use are: slower, have a much worse UI, and are far uglier. Kindle on
Android is just pathetic - it takes 5+ seconds to even launch (instantaneous on 4s)
The Android FitBit app does not even work without a data connection (work fine offline on iOS)
All apps scrolling is jumpy and sluggish on Android
The Droid X2 is running GB with a dual core 1GHz processor - better specs than the 4s, but much slower.
I had used Android for 2 years before switching to a 4s in October, and can't wait to swap back to my iPhone.