After the jerk at the Lexus dealer in Fresno screwed up my attempt to test drive the SC, I'm starting to consider the XLR.
Of course I'm asking the same question over on the XLR forum that I ask hear and I suppose I should just consider the source...that is to say, what forum that I'm asking the question on. I'm sure that each forum has its dedicated car owners.
Having said that, there is not one person so far on the XLR forum that would consider the SC or SL500/600...some of them have owned both and have said without a doubt the XLR is the way to go.
As a current owner of a 2003 MB E320 I can tell you that it had many problems, it's only now....2 years later that I have gotten all but one worked out.
I demo'ed a SL500 and while I was impressed with it's ride, power, transmission....I was not impressed that there were some squeaks in the are rests on the doors and some wind noise at highway speeds with the top up.