whats your favorite diesel pickup

There is a company by the name of "Groome Shuttle". The use E350 Extended Passenger vans that are all Diesels. They have been using them for decades. They put a ton of miles on them, and according to one of the operations officers, they would switch to another brand of type unless forced. I suppose that time is coming with Ford discontinuing the E-series vans after over a 50 year run, and only 3 major remodels and 4 body styles.
There must be a reason a company like Groome Shuttle", that depends on their vans being efficient locked into Ford Diesel vans so steadfastly.

...2 decades of continues operation with hundreds (probably thousands) of Ford E vans. Must me something to it.