Buy a 4S. You won't regret it
I am disappointed by the processing power and RAM in the 4th gen iPod touch to be honest. I constantly closing apps to make it run smooth. Coming from the iPhone 4 i was surprised (in a bad way) i think it needs more RAM to be able to run the latest games such as infinity blade 2 etc.
Trust that guy iPhone 4s is worth it. There is a reason it sells more than the iPhone 4 last year.
I got it and sold my touch and never looked back