I bought the Flash last Sunday. I had every intention of buying the S, but I just ended up liking the Flash more. Price had nothing to do with my decision.
However, if you need 16GB or feel the need for the 8MP camera, you can only get that with the S. If you think the larger the screen the better, you need the S. None of that applies to me. I actually prefer the screen size between 3.5" (iPhone) and 4" for my needs.