To be honest, they're pretty evenly matched. The Captivate does have a problem with GPS, but the iPhone does have a reception problem(even though not as big), and hardware wise, the only difference is that the Captivate is more durable and the iPhone's got the front-camera. In term of Android vs. iOS, the customization thing does go really far in terms of changing things such as the format of your screens, the different ROM's, overclocking the phone, different keyboards (like the magical Swype keyboard), and though the iPHone can be customized via jailbreak to do limitless things, the Captivate goes even beyond that to places Steve Jobs will never let you reach.
This standoff is more of a draw, I'd say, and you really can't compete with him on this matter. Best case scenario, drop both your phones on the ground at the same time and show him the magic your phone can do...