From what I have read, E39 530i MT is the best all around 5 series built. Taking in to account cost for ownership and maintenance, handling, power, fuel economy, build quality and a few others I'm sure I forgot.
I have a 97 528i and it's a great car. 530i if a refined version of my car with 30 hp more and upgraded look.
The late model ones look great dressed up. It's not a racer but a great cruiser on the HWY.