One is faster, decent battery, and heavier but has a larger screen. While the other is smaller, lighter, but has a slower wireless Internet connection.
You decide which is which and see how they will compare head-to-head in eleven days.
I think it's also important to note that the iPhone 4S will be sporting a more updated OS while the Bionic is running an OS that is at least a year old and while Android 4 is due out in November, it can take months before Android devices get OS updates.
Whatever camp you're in, this is fantastic. Competition. It's what this is all about.