When I load a PMDG 7478-400, I prefer using the cargo loader instead of the conveyor belt.
It shouldn't. All the configuration we made for all the PMDG 747, are all configured to use a cargo loader. None of them use a belt loader so, if you seeing one, it means you tried to change the configuration we made for the plane, so yours is taking over.
OR, you changed the configuration for the parking, as your screenshot seems to indicate.
I know I can select which option I can use
Changing the cargo loader type in the parking configuration is not the correct way to do it, if you want to change the airplane configuration everywhere. To do that, you must change the Airplane configuration instead, which is not required, since all the configurations for the PMDG 747 we made, use a Cargo loader.
The reason for having a loader type even in the parking customization, is to fix those *RARE* cases, where the parking is so small, that a cargo loader couldn't maneuver there, so you override an airplane settings to change the loader type or even disable it. But it's likely those parking spots would be too small for a 747 to use anyway.
Maybe, you have now made a lot of configurations already, which is why you see all Belt loaders.
but when I go to the menu where I can change it to cargo loader, it comes up as seen in the image. Looks like a mess.
I cannot reproduce the problem and nobody ever reported it. Your screenshot seems strange, as if you used an old version of Windows, or a classic Window theme, perhaps this is the reason. Also, try to use the editor in Windowed mode, not Full screen.