I always prefer using a Pennsylvania Crude Oil based motor oil, but since Pennzoil closed down their Oil City, Pa refinery last year it is hard to get a Pa-based oil. Valvolene is still Appalachian based as well as Penn-Brad at the old Kendall refinery in Bradford, Pa. But I've never used their's yet and don't know if I want to start in my Cummins. So, for now I am using Rotella 15W-40. I've used Pennzoil, Texaco Ursa, Kendall, Amalie, and Delo with success in diesels - all in either 15W-40 or 30 weight.
Blake