Hi,
I have an is200 as well as a xedos6.
I consider the 6 as the high quality /luxury car. It is more silent and has more luxury (seat heating, atm) where the luxury can be available in more expensive is200's and is default in the is300.
Advantage of xedos:
No problems at all for already 10 years. My is200 had a stuck cd changer, jutter in clutch, unstable idle speed.
Engine of the xedos6 sounds more smooth than the is200.
Advantage of is200: On the road like a train on rails. The xedos can absolutely not tip the cornering capabilities of the is200.