"BUT, buying synthetic oil has a big advantage, you're not funding terrorism!"
Great statement.
Anyway, based on what I have read so far, the best synthetic and most popular are Amsoil AME15W040 or Schaeffer 9000 5W-40 both are PAO or Grp IV based for mail order. Mobil One Turbo Diesel Truck 5W-40 available at Wally.
Schaeffer 7000 is also very good it is a blend of PAO and Grp III (highly refined dino oil hence synthetic also).
Rotella T Synthetic is also very good for Grp III.
Then all the dino, favorite is Rotella T but a lot of people like Chevron Delo, Mobil Delvac 1300S, Valvoline Blue.
One thing to make sure is that you get a Diesel rated oil (start with "C") instead of gas only rated oil (start with "S") when you go to Wally to get your oil.