If you are the passenger then go for the F430, you'll never ever forget the noise after the ride. The x-bow has an Audi engine, which is pretty quiet and hey you won't be driving anyway so you don't need to worry whether it's more of a track car than the Ferrari. Think of the noise!!
And to show a proof that I know what I'm talking about here's a video of me driving an F430 on a track in UK .
[YOUTUBE]http://www.youtube.com/watch?v=wITcQMtAPu8[/YOUTUBE]
Just go for whichever floats your boat. That's what I'd do.
After such a short time on the track you won't be making much of each car's performance either. The Ferrari might allow you to drive as fast as the X-bow much more easily if you keep the TC on. If scaring yourself a bit is important go for the X-bow, if you want some proper noise in a proper supercar go for the F430.
NOT the 911.
Because at some point there is a very good chance that someone you know, or you, will probably own one, and you'll get an opportunity to drive it in your life.
Go for the rarest car such that when you tell the story in the future you can impress people. Along these lines having to explain to a girl what exactly an "X-Bow" will be far less impressive.