go with either the Cummins or the Powerstroke.... the old IDI diesels wont hardly be worth your time compared to those two.

The first gen powerstroke will have the most stock hp, 215 ponies (excluding the 96-98 12v manual which has the same). all the other 12v's have anywhere from 160 to 180hp

But even though the powerstroke has more stock hp, the 12v cummins can make a lot more power a lot easier and cheaper