iPhone 3g. Bought it new yet within a month of purchasing it Apple released iOS 4 which slowed it down so much it might as well have been bricked.
That, plus the lack of OTA updates, needing to plug into a PC/Mac with iTunes (horrible app) to load music, backup photos or update lead me to never purchase an Apple product again.
Going from that to an HTC Android phone was like going 10 years into the future.