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I've driven (friend's) BMW 335i (coupe), and I can say that overall, it's a better car *ducks*. I liken it being carved out of a solid piece of aluminum. It felt solid, more isolated, and that engine is an engineering marvel.
That said, the 370Z is more involving, partially from the issues you mentioned (a bit more noise and ride harshness). Everyone here says it's a sports car, and it shows. There's less between you and the road - plus, it's $15k cheaper.
So as much as I'd give the 335i a nod in the "better overall car" department, I find more enjoyment out of the driving experience and prefer driving the Z (plus, here in SoCal, you can't throw your fob twenty feet without hitting a Bimmer
).