||kit, or are they still stock? If you haven't changed them yet, my first recommendation is leave your stock diff bushings alone... unless you have obvious signs they are worn out and causing problems.
If they are shot, then I'd recommend the Nismo bushings, if available. You'll benefit from higher durameter (sp?) rubber while retaining stock-ish NVH dampning.
Polyurethane will transmit more drivetrain noise. And solid metal ones obviously more still. Not ideal for what might be primarily a street car.