If you rule out large commerical diesels then Redline is Top Box!!! It is the most shear stable and temp stable oil you can buy. SOme large diesels engines builders do not want friction modifers in the oil. Delvac one does not have any friction modifers. Redline makes it's product in 5W20,5W30,5W40,10W30,15W40, 20W50 and straigt weights 5,10,20,30,30,50,60,70 as well as comopressor oil, shock oil,p.s..........THe 5W40 and 15W40 are specificcal made for diesel engines but not fleet type oils!
I doubt that most people would ever be able to tell the difference between the two products in actual daily useage. One point to remember is that Delvac 1 is an API rated oil so if you are concerned with warranty requirments that might be a factor. I prefer Redline products and do have a slight biasis but their products are not API compliant and that must be factored in!