I voted for the 335xi...
-Brand New (better warranty, service, resale)
-Better performance all around
-You get to pick all your options, color, trim, etc..
-Unless you're married with kids, a coupe is the way to go IMO.
The 530 already has 30k on it, you don't know how they treated their car, or how bad they were with clutch/tranny, etc...
Heh, I'm on a bit of a Euro delivery kick, but if you did ED, you can probably get the car for like $46-47k out the door including taxes. (Something to think about.