If you are looking for economy and reliability, the 240D is far superior in these areas as compared to the 300D. The 300D's have an extra cylinder that makes them more difficult to work on and they have automatic everything; climate control, electric windows, electric sunroof, on and on and on. On an older car, keeping these gadgets working can drive you crazy.
Most 240D's have manual a/c, crank windows, pull and shut sunroofs, etc. I have found that I really do have enough strength to wind up my own windows, and pull my own sunroof shut. I also have found that I have enough mental capacity to turn the temperature knob warmer when I am cold and colder when I am hot.
These manual systems on the 240D go a long way toward making these cars as trouble free as anything you can buy. If you get a manual transmission 240D, you won't have an expensive automatic transmission to go out and to soak up the additional torque offered by the extra cylinder. If your commute is 70 miles round trip, you are probably cruising on much of the trip rather than driving stoplight to stoplight. This means that the decrease in power is not as much of an objection. Once you are at speed, the 240D cruises as well as a big block Vette. You need almost no power to cruise.
There will be many that will post here telling that you must have the turbo because of the power. Remember, with that turbo comes many, many contraptions and gadgets that you will have to keep working.