I have them both. NJ International was made by a British company and it seems to be in 1:148 scale (still passable as one of the larger vans). Not perfect but it has the familiar shape.
Willmodels van is more suitable as a FedEx truck. It doesn't have the familiar rounded UPS van shape. Speaking of UPS vans, some of the newer versions are fugly Frankensteins of spare parts put together. Even uglier than the newest Dodge Sprinters.
One of my future projects is making the UPS van in N scale. But that won't happen for a while. I have a feeling that someone else will beat me to it (not that it is a bad thing).