Having had three Mercedes (the last being an S500) I became very unhappy with the build quality. I wanted a comfortable, reliable and well-made car.
Needing a vehicle I could step down from (age comes to us all - if we're lucky) an RX450 fitted the bill just perfectly. Its reliability has been flawless, it's a pleasure to drive, and mpg isn't bad either.
As an addendum, I was lent a courtesy car for the annual service - a UX, and have to say I was impressed, both with performance and mpg, for after a good 100 miles of mixed roads, it still provided 52mpg.