All the rumors are stating the next iPhone, the iPhone4S is not going to have 4G LTE capabilities, nor the NFC ability. So it'll have possibly better cameras, the A5 processor... Yeah, more of a bump of last year's model than a full revolution. All the speculation is you will have to wait till at least 2012 to see an LTE iPhone. So no 4G for you if you stick with the iPhone between now and then.
There are a number of different Android devices out there that run on 4G, whether that is HSPA+ on ATT, WiMax on Sprint, or LTE on Verizon. Just keep in mind that nearly everyone is going to an LTE standard within the next few years, not just the United States.
Android is a different beast than iOS. There is fragmentation, and every manufacturer seems to want to skin Android and put on their own widgets. Samsung has the TouchWiz, Motorola has Blur, and HTC has SenseUI... Sure you can get stock Android on most of these units by rooting at the like, but you are kissing your warranty goodbye. And despite what people say, they are not the same thing. When you pick up someone else's iPhone, you have a pretty good idea that it will function nearly the same as your iPhone, unless you did some modifications to the software. Pick up three different Android handsets from different makers, and ... yeah. You'll see. I don't really perceive that as a bad thing, options are always good. Just be aware there will be an acclimation period for any new operating system.