I used the iphone for 2 and a half years and then switched over to Android and never looked back. Android is a much more customizable OS in my opinion and it allows users so many more options. I personally think Apple fell behind with their OS, but the ease of use is there and thats why so many people like the Iphone. I am using the Galaxy Nexus after going through probably 10 different android phones in the last year I have to say it is a phenomenal phone. Build quality is excellent in my opinion, but no metal or glass. The screen is phenomenal, its 4.65 in with "retina display" pixel density, it kills the Iphones screen due to the fact that its a 720p screen PLUS AMOLED. I am using the GSM version so I dont have the LTW radio burning up the battery, so battey life is the best I have seen in any smart phone to date. And Ice Cream Sandwich OS is amazing as well. Super clean design, very fast, very intuitive.
If this is your first shot at a smart phone, the iPhone may be right for you, but I highly suggest the Nexus. The learning curve is there, but once youve learned it, you'll love it.