I have both MB and a Lexus and both experiences have been pretty good for the most part. Both of my cars were purchased new and now have about 150,000 miles on them each. I don't think you can compare the two cars the same. If you just look at reliablity, then the Lexus wins hands down. It has been relatively inexpensive to maintain and drives almost like new. However, if you want to compare them based on driving experience, then the mercedes is much more fun. I have logged all maintenance for both cars and the MB is about twice as expensive to maintain.
If I had to sell one of these cars and keep the other, it would be easy for me to keep the MB, but thats me, for people that only want a reliable car, Lexus is the way to go.