I've use Android phones since 2010 and the iPad 2 since the day of release, so I can probably give a somewhat objective analysis. IMO, Android probably does about 90% of what iOS does, while iOS does maybe 70% of what Android can do. So you gain some, you lose some either way (but you gain more with Android)
Honestly, there's only a couple major things iOS does that I care about that I wish Android did.
- multi-finger guestures. The 4 finger swipe sideways to switch back and forth through recent apps is pretty sweet, whereas on Android I have to hold the home key a second to bring up the list. It's nice on my iPad to (for example) have Tapatalk and Chrome open, then just 4-finger swipe back and forth. On Android, it's another press. I am assuming the iPhone has similar functionality as the iPad (I'm honestly not sure).
- tap-to-top: On my iPad I can just tap the black bar at the top (what I would call the Notification Bar if it was Android) and the web page or whatever app I'm in jumps right back to the top of the page. It's a nice feature.
- I honestly think Passbook looks like a nice program/app, and Android doesn't have anything like it. I can use Key Ring to store my reward and gift cards and stuff, and I use TripIt to keep track of all my travel documents, but Passbook looks like it takes those one or two steps further. Knowing the Android development community, I suspect we'll have a version of it within a month or two though. After all, Siri-like apps took less than 24 hours to start showing up after iOS5 launched (yes, there were voice actions on Android long before that, but nothing as "human" as Siri that I know of). I'm sure someone will correct me with an app that was out at the time that I wasn't aware of though.
- I have yet to find anything on Android that rivals the ease of use of their Airplay feature to send videos/music to the TV or stuff. Yeah, I have a bluetooth speaker at work for music, and I have a DLNA capable PS3 that I can send videos too, but Airplay is a far superior solution and I hate to say it...."just works" Of course, you have to have an AppleTV to really make use of it. Granted, I haven't really looked into the Google TV devices, so maybe they offer something similar. I plan on getting a Nexus 7 to replace my iPad2, so I'll be researching that a bit more.
- While not really an iOS feature, it's more something that comes with owning an iPhone: Accessories. Android phones vary wildly in size and shapes and even the location of the micro USB port. And while Android as a whole has a much larger market share than iOS, no single Android phone sells in iPhone numbers. Thus it's unlikely Android will ever see a dedicated aisle in stores for docks and stereos and things like you see for the iPhone. Like I'll probably never see a stereo I can buy where I can just slide my Galaxy S3 into a slot at the top to connect it, so I stick with bluetooth enabled stereos, which is fine with me. Maybe someday manufactures will realize if they try to standardize some of that, they could also build accessories to sell us (like I'd buy a Samsung stereo with a dock if I knew that future versions of the Galaxy would work with it).
- Going along with the above, there is also the issue of certain models of cars or stereos being build with the iPhone specifically in mind (so you plug it in and the music you're playing shows on the car's stereo display and you can use the steering wheel controls to change tracks and stuff. Nothing like that for Android that I know, but my understanding is that Apple's new proprietary connector (Lightning) removes this "iPod Out" functionality, even with the adapter, so those car stereos won't work anyways. I'm sure all those mini-cooper and BMW guys will be happy when they buy their new iPhones and $30 adapters and the stereo doesn't work like it did any longer. Again, I just connect my Android via a headphone jack to my stereo (I'd use Bluetooth but I don't have a bluetooth stereo in my car). Sure I can't use my steering wheel controls to change the track, but it's not a dealbreaker to me. Maybe there are some Bluetooth stereos available that would allow the same functionality from an Android phone....I don't really know since I've never looked.
That's about it as far as major features I care about in iOS that I wish Android had (obviously there's some smaller things here and there as well), and that being said, Android does a TON of stuff that iOS doesn't do and completely blows it away. I'd rattle of a list if I had more time, but just look at the list of things Tasker alone can do that the iPhone only wishes it could. Or a "Find my Phone" app like Cerberus that blows away anything iOS has (ability to remotely take a picture or video or record audio from your stolen phone).
This is something that's often overlooked in Android, but I can't stress enough how important and awesome it is. You know how one of the major features of iOS6 is going to be Facebook integration (so it's going to have BOTH Twitter and Facebook)? You know what I had to do to integrate Facebook? Install the app. You know what I had to do integrate Twitter? Install the app. Dropbox? Install the app. Take a look on your iPhone and open up the gallery, choose a picture and press "Share" and see how many options you have to share it with (Tweet or Email are the only true sharing ones). If I do that on Android, I have roughly 36 options that include Email, Text, Flikr, Instagram, Google+, Picasa, Facebook, Twitter, Dropbox, Google Drive, Evernote, Foursquare....the list goes on and on, And all I had to do was install those apps to integrate them. That's it. I actually laugh at iOS touting Facebook integration like it's something groundbreaking. Scoff, even.
As far as FaceTime, the Google+ Hangouts blow it away as well, and works across devices (including iOS). Not to mention Skype and everything else that works on everything. The trouble is convincing your iOS friends to use something besides FaceTime.
I have an S3 as well (the phone you're considering) and I think you'd be very happy with it.
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