Ah, I double checked and it was for verizon. 4.1.2 has some very nice stuff like the quick access to settings, Google Now, Photosphere (and much better camera controls), and built in swype-like input for the keyboard. Not sure when that's hitting for the S3 though.
Can't help you on swiftkey, but a quick google search suggests it doesn't work in all apps. Is it fucking up across the board for you?
I got a badass camouflage Otterbox Defender and it works great. The problem I had with my other one is I was dumb enough to keep taking it out of the case, making the rubber lose it's shape and the case was then able to get dirt inside it. If you only take it out when you have to it should work perfectly.
One thing I would suggest is using a custom launcher, if you haven't rooted it or are wary of doing so. I use Apex Launcher on my HTC One X and it works great and looks so much better. That is if you download themes for it that come with nice icons. A lot more features than the default as well. I personally wouldn't risk rooting it purely because it voids the warranty which is why custom launchers are always good to dabble with, and if you don't like it or want to try another you can just uninstall. When I accidentally close mine down and it reverts back to default I still can't believe how ugly it looked the whole time I used the default haha.