This is a debate that will go on until the end of time.
Most diesel owners are convinced they already know the answer, and there is little room for debate from their perspective. There are a few, however, who are enlightened enough to see the virtues of both arguments.
Gas models cost significantly less than diesel models - on the order of $80k-$100k less when similarly equipped and sized. For instance, the similar in size and featured Tiffin entry-level RED (Rear Engine Diesel) comes in at $95k more than the upper-end gas model we are pretty well set on. For that $95k, you get diesel power and a smoother ride, and two additional slides. So while the extra power and comfortable ride might be nice, we don't want the extra slides. Given that, are the above features worth $95k?
Our answer is no. Your mileage may vary.
The Case For And Against Gas
For: Cost of ownership is much lower. Regardless of the initial purchase price difference, annual maintenance is much cheaper on the gas chassis. Most shade-tree mechanics can do their own oil and filter changes and lube their chassis without having to bring the motorhome into a large truck shop. Oil is measured in quarts - not gallons as the diesels are. A typical oil change will run anywhere from $50 to $75 max on a gasser.
There is also no fuel filter to change on the gas chassis. Gas is usually anywhere from $.20-$.50 per gallon cheaper than diesel fuel.
Gas models are quieter in the campground when coming and going.
Against: Gas models lack the power and torque that some diesel models have. That being said, depending on how heavily loaded each vehicle is, sometimes diesel motorhomes are passed by gas motorhomes going uphill. It depends on a lot of factors.
Which brings us to engine noise. On gas motorhomes, the engine is up front, and there is a "doghouse" assembly sitting between the driver and passenger seats. In essence, the doghouse is an engine cover, which can be well insulated for noise and temperatures, or badly insulated. Either way, having your engine underneath your feet will make for a fairly noisy ride at high RPMs.
Gas engines do not have the lifespan of a diesel engine. It's not uncommon for diesel engines to run well, even after a million miles. Gas engines are typically good for upwards of 250,000 miles, depending on how well they are maintained.
Gas chassis ride harder than diesel chassis. There is no getting around the fact that these are basically truck chassis, with typical shocks and leaf springs.
Braking power can sometimes be limited when the gas motorhome is going downhill, especially at max weight.
There is sometimes (but only depending on model types) less storage in the basement of a gas motorhome due to the driveshaft running from front to back. However, some models like the 36LA we're sold on, have more overall storage than some entry-level diesels, only suffering in the size of the pass-through bays.
The Case For And Against Diesels
For: 450 or 600 horsepower engines provide a LOT of power and torque for going up mountains. Diesels also have an engine brake (sometimes referred to as a jake brake) that helps to slow the motorhome down dramatically and assists in stopping the unit much quicker. It's that throaty growling sound you hear many big rigs make when decelerating.
Diesel brakes are air assisted for shorter stopping distances.
With the engine in the rear, diesel owners do not hear a lot of engine noise when driving down the road.
Diesels have independent suspensions and air bags underneath to smooth out the ride.
Because the engine and transmission are in the back, the center basements of diesel motorhomes are large, pass-through storage with pullout trays for easier access to larger items.
Diesels will have higher-end finishes and amenities, like better woodwork, heated tile floors, dishwashers, and more seating and sleeping space due to their longer lengths.
Diesels generally have towing capabilities up to 10,000 lbs, instead of the gasser's 5,000 lb limitation.
Against: Typical maintenance of a diesel coach will be in the thousands of dollars annually - if you want to make it last for as long as possible. And there's more of it.
Diesels make a LOT of noise coming and going in campgrounds, especially those who want to get an early start to the day and like to idle their motors before moving (something they don't really need to do, and actually harms their engine more than if they just drove off).
Bottom-line: As with everything in life, there are trade-offs. And it all depends on what you're going to do with the motorhome, and where you're going to go. If you're going to spend a lot of time in the mountains, maybe that diesel is the way to go. If you're full-timing and don't have to be at a certain place at a certain time, that gas model will work just fine for you. If the ride is too bumpy for you in a gasser, there are suspension mods that might cost as much as $12k that will make it better, but will never get you to the comfort of a diesel ride.
Oh, and every motorhome sounds just the same with jacks down and slides out sitting in a campground.
Barbara and I decided that we can do a lot of sightseeing and glamping with that $80k difference (we'll be doing the suspension mods) between the diesel and gas models we like.
We're Dave and Barbara Richard, and we're living the ultimate retirement experience - traveling the U.S. and Canada in style in a Tiffin Open Road 36LA Class A motor home, playing golf and stopping at every weird and wacky roadside attraction we can find.