This was hashed out on the View/Navion forums. The winner? The diesel generator, by far. The people who have one say it doesn't smell, and some just use a Gen-Turi system so the exhaust is dispersed over the top of their rig, so it isn't an issue in any case.
You will hear dealers say that it is easier to use propane, propane smells better, and so on. Dismiss it. They just want to sell their rigs that have LP gas gensets. Propane can be a PITA to get, and it is a lot harder to take extra along than a few extra cans of diesel on a hitch mounted cargo rack.
If given the choice, go with a diesel generator. You will be happy you did.