The Galaxy S3 is just around the corner (gets released internationally at the end of the month)
As for which is better out of the S2 and IPhone 4?
I've had an S2 and an old iPhone 3g , the better half has an iPhone 4. I found the S2 to be brilliant when I first bought it. The screen was massive, the android OS is so much easier to use than iOS (no iTunes, YAY!) and I could watch mp4s on it without having to further convert them using iTunes which is a great help if you do long plane or bus journeys and like to watch movies. File transfer is also a breeze - just drag and drop and it would read most files. Oh, you can also view websites that require Flash (i.e smut
) which is something Apple are STILL incapable of allowing us to do.
Sadly it's also a flimsy piece of shit (the back panel falls off all the time), the battery life isn't great and in my case proceeded to get a lot worse - I'd get maybe a couple of hours if I was lucky on normal use and it even completely drained once during a shift at work where it had been put both Flight and Sleep modes and left in my locker. Due to this and an issue with the mic I sent it off to be repaired under warranty however the service centre claimed water-damage and wouldn't repair it. This is utter bullshit as it had never been immersed in its life - they do claim that it can be humidity that can trigger the water-damage indicator in which case, if the phone is so badly designed that humidity automatically voids the warranty then I'd have serious doubts about buying another one. Having read all the reviews of it though I suspect I may have been sold one with a dud battery as there is no way it could get such good reviews with the battery life I experienced
ON the other hand, my missus' iPhone seems to be working fine and my old 3G is practically indestructible and has indeed been immersed in water and still functioned after drying out a few hours later. The battery life isn't great on the 4g however and the screen is a bit small for my liking. You've also got to put up with iTunes when you want to add/remove files. The iPhone is also a couple hundred bucks more expensive (maybe not an issue if you're on a plan) and other than the handset design -which is actually a bit blocky for my liking - you're not really getting anything extra.
In conclusion, it really depends on what you use your phone for. If you like watching movies when you're travelling (and don't have a tab), not being constrained by iTunes, being able to use your phone as an external hard-drive then get the S2 and possibly a multi-use battery pack to top it up when it exhausts itself an hour later. Don't bother getting an extended warranty though. The cheating bastards probably won't honour your original one.
If however you want something that is extremely well made physically but comes with an operating system that's a bit of a pain in the arse, then get an iPhone.