"Without considering price." Many people make decisions according to what fits into their budget but since this isn't a main concern for you, I would personally take each car for a test drive and keep each car for almost an entire day. Ride all over town and have others ride along. After rigorously test driving both cars you should have enough insight to make a decision on your own. I'd definitely get the GS430 b/c I enjoy Lexus quality, service and saving money. :D
Take a look at this link: http://www.edmunds.com/new/2006/mercedesbe....Mercedes-Benz*
LOOK CLOSELY AT THIS POST: "I have had my CLS500 w/ AMG sport package, keyless go, satellite radio etc. for going on 8 months and it has been in the shop numerous times already. On average, once every 2 weeks and one time for more than a week."
Just something to think about....