I have been driving a 94 LS400 for 3 years. I want to replace it with 04 BMW 545 or benz E500

I would avoid a BMW or a Merc unless you find one fully loaded. I'm also assuming you've already considered a newer Lexus (like a 200+ LS400/LS430). That said, I've never been a big fan of the E-class Mercedes, so I'd pick the 5-series. But I'd be more specific as to what you're looking for in the car. Also, give us an idea of your budget.

You mention "I like the fact that it does not have to go to the shop a whole lot." Most likely, you will have the opposite experience with a Benz/BMW. Don't get me wrong, the Germans make a nice product. If you are planning on purchasing one used, it is crucial that you get a good warranty (no matter what you get), because when things break, you'll be breaking the bank to fix them. The LS is aimed more for 40-60 year old golf playing men. However, Lexus does offer some more "hip" alternatives, such as the GS or IS. The GS is the closest Lexus competitor to the E-Class and 5 Series. I have had both a Benz and a Lexus, and I will admit, the German cars were more fun to drive. But in the long run, the Lexus blew the enjoyability factor off the doors of the Germans - you'll never have fun with a car if its always in the shop. Hope this helps and best of luck. - Mark