I have driven both...I drove a BMW 325 and was much more impressed by it's smoothness than the IS300. And I don't base my life on stats. However it's Lexus' own fault for not including a manual transmission in their line up. So until the IS300 delivers a manual transmission (or Lexus delivers a real shift box for that matter), as far as I'm concerned, BMW has the edge over Lexus.
Even Mercedes went around their own beliefs and included a manual transmission in their new C240.