For me I would say the iPhone 4 if you weren't affected by antennagate, it was so... game changing. Retina display, a4 processor, square glass design, front facing camera, facetime, hd video recording,gyroscope etc.. Then the iPhone 3g pre iOS 4. Good stable phone and the first iPhone to have 3g tech. Then the iPhone 5. Taller screen, 4g, dual band wifi, 3 microphones, lightning charger, two tone design, relocated headphone port, a6 processor. It is one of the most changed iPhones.