I'm on T-Mobile but have to buy the phone unlocked because I'm on prepaid.
The other thing that worries me about switching to Android are the updates. I don't want to be using a device that isn't being updated. With Apple, you generally get updates for 3-4 years, which is great and about the maximum to reasonably expect.
With devices like the Galaxy S2 and Galaxy S3 having delays in getting the latest firmware, that seems unacceptable to me. And with the Galaxy S, the Android equivalent of the iPhone 4, not getting Jelly Bean, that doesn't seem good to me. Maybe there's a good reason for that, but why have that on Android when I'll likely get the updates instantly (albeit stripped) on iOS?
My personal take on updates is that they are nice. Unless there is something that I seriously need or want in an update, I do not feel in any hurry to get an update. I have a Galaxy S3 and I am perfectly happy with it running on ICS. JB is due out later this year and the only thing that I would think is nice is Butter. Still, even without butter, I have no issues with its smoothness.
When you had your iP4, what was it with each new update that you really couldn't have waited a few months, say, to get? You said you didn't want much from a phone, so what could it be with each update that you actually wanted?
In any case, I am not going to convince you to get an Android phone. From your initial post, you didn't indicate anything you didn't already like about your iP4 other than the fact that it is 2 years old. If it is still working for you, why does it matter if it is 2 years old. If it is a matter of fashion, say like how my wife may feel, then just get the new iPhone 5. It would be an easier transition for you than getting a phone that runs a different mobile OS. If you can tell us why you are dissatisfied with your iP4 other than the fact that it is 2 years old, then we can be able to tell you if an Android would be a good choice for you.
I'll give you a summary of why I chose my Android phone over an iPhone in the past few years:
1. I initially wanted a phone with a landscape slider keyboard. There is no iPhone that has one.
2. When I last upgraded, I got an SGS3. I did not choose an iPhone because I would lose widgets. Widgets are very useful. I have one that when I tap it, it would turn off all notification sounds, but leave the ringer and alarm sound on. I use this when I go to be. When I wake up, I tap the widget again to turn notification sounds back on.
3. You can do more customisation with your phone. I use Nova Launcher to change my home screen. I did not want that dock of icons on the bottom of my screens, so I got rid of it and added an extra row of icons with each home screen.
These may or may not interest you. If they do, feel free to ask us more about it. If not, just stick to your current phone or get a newer iPhone.