If you're considering getting a phone this fall, you might want to consider
Windows Phone 7, due sometime this fall. Previews indicate it's as slick as Android or iOS and is comparable overall, with some positives over them and some negatives. Initial U.S. carriers will be T-Mobile and AT&T.
I do agree with mdwh that this isn't a two-choice option; I know people who are excited about the new Blackberries, and they certainly aren't the media's favorite phones these days. Having cast my lot with a dumbphone with better multitasking than an iPhone 3G, though, I don't have extensive experience with any smartphone OS.