Two Honda 2K's is not the most fuel efficient. The advantage to the 2 Honda's is the 65 pound weight of each.
A single Honda 3K IS is more efficient then the above example, but it weighs 130 pounds.
Using the above example, one 2k Honda will use less fuel, but not much less then the 3K
The 2K Honda is not as quiet as the 3K at any load. And at near max load it is about twice as noisy as no load.
The 2K has a significantly smaller fuel tank.
In the BTU content arena it is (high to low) diesel, gasoline, propane.
Convenience - gasoline, diesel, propane.
Storage (quality) propane, diesel, gasoline
Storage (safety) diesel, propane, gasoline
Given all that, if I could, I would op for one of the quiet diesel gens with a fuel cell added to the trailer.
The quiet high end portable diesels are still fairly large, and heavy.
Our new plan for the week long boon docking at Dover will be to bring the Honda 3K along for most of the needs and only use the on-board Onan when we need the extra power. I figure that will cut the fuel usuage at least in half.
The Cyclone has a 25 gallon on-board fuel tank, so that makes gasoline less of an inconvenience and I will be getting one of the commercially avaible totes (14 gallons) for re-fueling purposes.