All three are proven diesel oils. Seems to me they would all be reasonable candidates. Assuming that he would not experience any significant difference in using either of the three options, I would rule out the most expensive one.
That leaves:
- Valvoline Premium Blue Extreme, available from Amazon, Walmart, O'Reilly's for ~ $29 / gallon.
- Shell Rotella T6, available all over the place around $22 / gallon.
Any discounts, rewards card points, store gift cards or shipping costs in play to consider?
I have not personally used either one, only the conventional mineral oil 15w-40 of these two. Just added the Valvoline to my Benz yesterday, so can't really comment yet on it.
But the Rotella T4 performed well for me, just as advertised. The T6 is the least expensive option, which is a bonus. He may need to add some oil at some point while out on the road. If so, that Rotella T6 is only a Shell gas station, WalMart or auto parts store away.
So putting on my oil consultant hat, if you were my neighbor, based on my own experience with T4, I would point you towards the Rotella T6.