I would go with LS400. According to one news report, a 10 year old LS is more reliable than a new 7 series.
The tecnhology in the W124 is from the late 70's, and is no comparison for the LS, in ride, handling, safety and comfort. Also, LS is far superior in noise, vibration and harshness levels.
As for the W210, I drove a 01 E55 AMG and was not very impressed.
I have spent some time comparing the systems on the 95 LS and 94 E, and the LS is very immpresive. Cost for the repair parts vary, AC compressor is cheaper for the LS but the Air Flow Meter is a whole lot more expensive for the LS. At the same time, the design on the LS is such that it will work for 500,000 as opposed to the E, where it needs replacing every 60-100,000 miles.
You can buy subscriptions on
www.alldatadiy.com, compare the systems on all the cars you are interested in, find out what the repair parts costs and how long it takes to replace them along with service bulletins.
I would buy a 98 or later LS400/430. In 98, five speed transmission was introduced, along with Navigation and the updated V8 produces 290 hp.
An overview of forums below will reveal that the LS has very few and very different problems then the E!
http://us.lexusownersclub.com/forums
http://www.clublexus.com/forums/index.php