My husband had an iPhone and then switched to a droid. I liked it at first, but recently switched back to an iPhone 4s. His reasoning was that with the iPhone "the user experience is easier".
I recently switched from an iPhone 4 to the 4s and LOVE my new phone. I was pretty taken with my 4 too though. I have noticed that it's a little bit faster, but not significantly. The camera is wonderful! As for battery life... I leave my phone charging on my night stand over night and when I get up in the morning it goes it stays with me all day. I am constantly fiddling with it, doing this or that, and right now (about 14 hours later) my battery is at 51%. Now, that can fluctuate if I am using the iPod portion of it very heavily, but it's not a major issue, IMO.
I hope that helps and gives you at least a little more info to go on. Good luck in your search. Whatever you get though, make sure it fits YOU and what you want/need in a phone.