I'm biased. Go for the 300SD. I had one, all too briefly and loved it.
Consider rebuilding the driver's seat. The springs and padding designed to be replaced to restore the original comfort for low $$. Get a quote from PartsShop here.
Be sure all steering/suspension items are good, such as shocks and bushings. Then, aim that 3-pointed star at your destination and cruise all day long at 25-27 mpg!