I really don't think 8gb will be enough for most people, especially over the life of a 2 year contract. I bought a 8gb iPhone 4 on Sprint last summer when I broke my Pre 2 & needed a new phone right away. It was only $50 at Best Buy, and I had a $50 gift card, so I was like, I'll take it!
Man, did those 8 gigs fill up fast. It got so tiresome trying to micro-manage the space too. Constantly monitoring the photos I wanted to keep on the phone, the music I wanted on it, which apps to update. Sometimes I wouldn't even update apps because I had no space. Another drawback was that whenever apple pushed out an update, I would have to update the phone via iTunes, because there wasn't enough available memory to do it OTA.
The final straw for me was when I was at a friends wedding, and was recording a video and the phone ran out of memory. By the time I deleted some pics to free up space, I missed the moment I was trying to record. Not too long after that, I went on eBay and bought a 64gb iPhone 5 off contract. Couldn't be happier.