My main phone is a iPhone 4S on AT&T which I upgraded to from a 3G model. As one of the posters above stated, you are very much watched over by Apple in terms of what apps or content is available to you. If you don't care for Apple this can be a big deal.

I bought a Android based Samsung phone last week, to have a second, unlocked phone, for travel use with local SIMs since I don't want to JB my iPhones.(I also just wanted to buy a new gadget) In setting it up I discovered that it's pretty much impossible to update to download apps from the market place unless you have, or sign up for a gmail email account. If you are a person who dislikes Google, then this might be a reason to shy away from Android.

For my use which doesn't include tethering, and includes a lot of WiFi connectivity, I don't notice the data on the iPhone 4S being slow, unless it's in a Edge or GPRS area. The 3G and HSDPA connectivity is plenty fast for me.

On the Android phone I bought, there's an app that does voice recognition searching, and you can get a text to speech app as well.

I think both platforms are good, but where you will get locked in is when you buy content like apps and entertainment from one of the vendors, and also the investment in accessories and for some the time to learn how to use it.

Absent a particular must have app, or a support or non-supported dictum from work, I think most folks would be happy with a new smart phone of either variety. That makes the advice to get one that uses a network that has a good signal in your area an important thing to consider.