Iphone 4 or Iphone 4S

Hi. I'm closing out my T-Mobile account by November (Thank God). The HTC Mytouch 3G is the worst phone ever. I won't buy an HTC phone again. The android network's apps are not as good as Apple's applications. I'm thinking about returning to ATT by next month. I'm just saving up for the phone right now. Anyway, I don't know what to select. Iphone or Iphone 4s. Logic would dictate that I select the much newer version of Iphone. I plan to buy this phone at Walmart. They sell the Iphone 4s for $188 and the Iphone 4 for $88 only. I plan to sign up for the $39.99 plan with $15 a month for data and no text plans. This would be about $60. That sounds good for me. I don't use the internet on the phone anymore except for checking in on foursquare or facebook. I'm just gonna use this phone to talk to my friends and my family. As for taking pictures. The 5MP is decent for me. Since I have a video cam and a camera that's capable of taking pictures at a much higher resolution. My video cam and Camera are also capable of taking HD Videos at 720 and 1080p. So is the 4s worth buying? I know for the fact that they've added Siri and upgraded the camera for this kind of phone. If I just settled with the Iphone 4, I won't be missing a lot right? I just want to hear it from iphone 4s owners if switching to the 4s is a much better choice. Thanks.