Which iOS works best on the iPhone 3GS?

Which iOS works best on the iPhone 3GS?
I recently bought a fairly little used iPhone 3GS which still has the iOS 3.1.3 installed. However some of the apps that I use require at least iOS 4.1. Aside of that I would like to have the possibility to turn off/on cellular data as I wish (feat not available on the iOS 3.1.3, it's always on). I heard some nasty stories about 3GS-es getting troublesome after having been updated to iOS 6.
Can you good folks drop a piece of advice on if/how I should update my 3GS?

Look this http://forums.macrumors.com/showthread.php?t=1229842

  • Which network works the best with the iPhone 5? I'm currently with T-Mobile, but switching to a new network soon. Which of these networks works the best with the iPhone 5: AT&T, Sprint, or Verizon? And what makes it better than the others?
  • Which iphone should I get? Which one is the cheapest with the best picture quality? Hi, I'm looking for a phone good a great photo quality. I was looking into getting an iphone… But would anyone say there are other phones that are better? I'm hoping to buy the cheapest one and right now my options are getting the iphone 4s on a $0 plan or investing a bit more money and getting the 5c… Do you think its a good investment?
  • Which iPhone should I get & which one is honestly the best? I have used and bought a lot of apple products but this will be my first time getting an iPhone since almost EVERYONE has one now. I really want to try. So now that the iPhone 5 came out… Which iPhone is the BEST? -iPhone 4 -iPhone 4s Or -iPhone 5? I've been hearing that iPhone 5 isn't as great as they make it seem, is that true? If it's not then should I get the iPhone 4 or 4s?
  • Which iPhone is the best? Which one should I get? I'm getting a new phone and currently i have the iPhone 4. What are pros and cons of each iPhone, what do you recommend?