For city driving, S320 is a great car. One of the guys said its underpowered, thats a typical Detroit mentality. Most of us are used to heavy 5.0L engines that perform extremely poor.
The S320 is a well engineered machine. Its has a decent speed and its fast. Besides its easier to maintain than V8s or V12s.
Now to your question, S and E are two different animals. S is a bigger car with various different electric controlled modules that can go wrong. If you can find one with starmark warranty, great; if not then be prepared to spend extra cash every quarter on maintaninence. Best bet is a 97 plus model. There is a big leap in technology and class in E and S classes. My 1996 S320 still has its orginal invoice of $67,000. A 1999 E55 is about $50,000