This question can really only be answer by the user. Some thoughts though:
1) UI-Two total different approaches. Android lets you customize pretty much anything you want, while Apple continues to keep you in the box. Now, is the end result really that different? At the end of the day, I dont think so. You have to do more poking around in IOS to get to information or settings, but the functionality is pretty much the same. The biggest difference is connection to information. Android will update all day in the background, meaning that the widgets give you real time info. On IOS, you have to go into the app, and let it update before you presented with the information you are looking for. This plays a major part in..................
2) Battery life-IOS hands down has better battery life than Android. IOS, when not being used does pretty much nothing other than pulling emails and Text messages. No updating of stocks, weather, news or anything else is happening unless you go into the app and open it up. Android will automatically bring down info on a schedule that you determine. It can be once an hour, once every for hours and so on.
3) Camera's-For Android it is hit or miss. Motorola's camera's are not that great, while the Samsung Galaxy S2 has a camera equal to or better than the Iphone 4S.
4) Web Browsing-Android beats apple. Its not because of flash, which IMO is not that big of a deal. Its in text reflow when you double tap to zoom. The safari browser formats the pages for a one stage zoom. the Android browser will reflow the text when you double tap so that the text is much larger and easier to read. On some web sites, I have to turn my 4S into landscape to make the text big enough to read which is annoying. In terms of speed, both browsers are fast enough.
5) Apps-There are virtually no apps not availble in the App Store that are available in the Android Market. The Android market has almost all of the big name apps that the App store has with the exception of games. Tiny Wings and Infinity Blade are two that jump to my mind. Apps that are on both Android and IOS are very similar though. Both have good UI's and are stable.
6) Stability-I would say that both are pretty much on par. I have used the GS2 recently and it was flawless. Never had any issues with the phone not working. IOS is also rock solid. I dont see the stability issue being a major selling point anymore. The latest Gingerbread builds are great and ICS is another step up.
7) Fragmentation-Absolutely an issue on Android. Many apps that are released only work on certian devices. OS updates are painfully slow. I believe Samsung has about 7 differnt models running on 50 different carriers. Each carrier has a slightly "tweaked" version of the touchwiz interface. Thats alot of differnent devices that have to be updated which explains why it can take 6 months, or more, to get an update. IOS, is obviously the opposite. An update comes out and you get it right away. Buying apps is also becoming a more frustrating experience on Android. Android has the Market, the Amazon App store as well as several app producers who only sell on thier own web sites. This makes finding an app frustrating. The app store is your ones stop shop. No fuss, no muss.
8) Sycing-Itunes remains the gold standard for ease of syncing your music and movies. Each Android OEM has their own version of syncing software and quite frankly, they all suck.
At the end of the day it comes down to personal preference. For me, battery life is pretty much the most important factor. I have yet to find an Android phone that comes close to matching IOS. My GS2 would discharge at a rate of 6-7% an hour.(14-16 hours until dead). And that was with light usage. My Iphone, with the same usage patterns discharges around 4-5% an hour (20-25 hours until dead). Thats a huge difference.
My advice, as always it try them both out and see which ones works best for you. Its not longer a function of which is better, its which is better for that particular person.