Tech specs tell only part of the story, but I'll start with those. Anandtech had a complete review of the Galaxy SII and without question, it appears to be one of the best (if not THE best) Android phones. When thinking about how it might compare to iPhone 4S, there are some important observations to make:
1. Most of the CPU-bound tests, the dual-core S2 was beating the single-core iPhone 4 by 25-50%.
2. In GPU tests, the new Apple GPU as demonstrated in the iPad 2 utterly dominates the other devices: http://www.anandtech.com/show/4686/sams ... defined/17
3. Battery life. iPhone 4 dominates and iPhone 4S claims to have improved on that.
The other part of the story is the OS. Android has been reknown for having beefier hardware and better tech specs, but because of [a multitude of excuses], it has also been notorious for having a variety of performance problems ranging from SCROLLING (how basic is that??) to MULTITASKING to network performance etc.
This guy's observations give much better insight than I have time for here: http://daringfireball.net/linked/2011/1 ... th-android
Some other stats for you: http://www.readwriteweb.com/mobile/2011 ... others.php
Overall, there are a lot of interesting dynamics at play. Android is ever-changing, ever-improving and varies greatly depending on device, carrier, and personal software preferences. From experience, Android is more of a dream / idealistic product versus being actually complete and fully usable. Android users are "loyal" because they believe in the dream and believe that every new upgrade is better. And every update is better, don't get me wrong. But even the latest Android OS has issues with some of the most basic functions.
By comparison, iPhone has a unified ecosystem that is stable, performant, and consistent. It may not claim to have all the features or "openness" that Android promises, but what it does have WORKS and WORKS WELL.
Some day, Apple will have some real competition in the mobile phone space. But I don't think there REALISTICALLY is a decent competitor out there that offers the same stability or performance or even apps that Apple has.
My predictions are that 2012 will be a big year. We are looking at Windows 8 and the ecosystem that Microsoft will successfully construct - almost overnight. We're also looking at Google + Motorola, and the possibility that there could be something other than Android - a vertically integrated solution just like Apple's in the works. And Android will certainly continue to grow and enhance. Supply of mobile components is reaching critical mass.
Get the iPhone 4S, and then take another look at the market in 2012 or 2013. There will be more options out there and you will actually be able to confidently look at one or two potential alternatives.