Just thought I'd add that if you are going to be into rooting and want to tweak your phone, it is definitely worth taking the developer community into account. The S3 has massive community support, both for modified stock ROMs as well as other AOSP ROMs such as C, and will more than likely do better in the long run than the HTC devices (particularly the One S). I personally would have waited for the Nexus phones if I had the option to, but the S3 was/is good value and the developer community does mean that releases of AOSP ROMs should be pretty darn fast once the Samsung source is released to sort the HW Composer issues. Personally will only run CM on this phone, so it doesn't make a huge difference whether I buy a Nexus device or not, as CM is always built from source.
I spent a long time looking at the different options and of course, decided on the S3, namely because of the better battery life, community support, and reliability (poor HTC service experience in the past has caused me to stay well away from HTC again, and the One X had some hardware issues that I'd rather not risk). The One S would have been an option provided the display was better, though of course, whether you get an S3 or S4 One S makes all the difference.
If you aren't into rooting, do take a really good look at all of the devices in store, and don't make a decision based entirely on what you read. While most find Sense absolutely fine, many are completely split on TW - after trying to use it again yesterday, I just find it absolutely terrible.
The iPhone is a great phone and the only true "it just works" option, but if you are not using your 4 to the fullest, I really cannot see how buying a 5 will make a huge difference (aside from being quite a bit faster). It might be worth saving your money here, but that's for you to decide. Worth saying that while apps are still slightly better on iOS than on Android, one-by-one apps are really improving on Android now, and Jelly Bean is a huge step forward for the platform IMO. This said, I'd say that none of the other devices will match the iPhone as a whole as complete, polished products, and while iOS is less flexible and more restrictive, it is equally as good an experience.