The iPhone 5 is a fairly big update over the iPhone 4S. It's an all new design, bigger screen and much lighter and thinner. To be honest, if you're not interested in the bigger screen, or plan to use the much more powerful internals or 4G, you're best going with the iPhone 4S.
If possible, try to get to an Apple Retail Store where they have all the devices on display for you to see and play around with. The staff are always very friendly and experienced, so they can guide you on what will be best.
But, you need to make the decision yourself, here are some links to help you out:
iPhone 5: http://www.apple.com/iphone/
iPhone 4/4S/5 comparison chart: http://www.apple.com/iphone/compare-iphones/
Apple Retail Stores: http://www.apple.com/retail/
Hope this helps!