I'm gonna throw my vote in...
G35 (waits for flatty to chide me for not picking the merc). 350Z with two spare seats, all the goodies, and you can get them factory with Brembo brakes. What's not to love?
The last three really aren't luxury cars, in my opinion. My next vote would be the volvo, though I'm not a fan of an awd turbo sedan that size with the wrong way facing engine. The mercs have just started to get their reliabilty back to where they were 15 years go and any cars built between 1997 when chrysler sold them will have reiliability issues (why I believe chrysler single-handedly attempted to kill mercedes).
the 2.0-T sedan would be nice from Saab, since it's basically a subaru with pretty leather and what not.
Everything else is pretty meh, I mean Audi's feel like they're carved out of lead and I don't think that much vehicle weight should be hauled around with the little 2.0L motor.
BMW's are alright I guess, I mean I've never been a fan of them, maybe I've just never been a fan of the stereotypical Bimmer driver, who knows.