My particular field of expertise is iOS Jailbreaking and Unlocking.
Well the iPhone 4 is definitely one of the cheaper models of the iPhone at the moment. But if you're willing to pay for an iPhone, the 4S or the 5 would be great. They running a bit faster than the iPhone 4 plus you get Siri and such.
Hi, and welcome. You can get an iPhone 4 for 99 cents from ATT (online) with a 2 year contract. A fine deal, since the iPhone 4 is just fine. But that 2 year contract is the biggie.