Gas or diesel class c

Diesel C today means either something about 25 foot long on Sprinter, RAM Promaster, or Ford Transit, or else a Super C on something like F-550, Business Class Freightliner, or medium duty International. Or if looking used, on Kodiaks, but many of those had the 8.1 Vortec engine rather than the Duramax, probably because of the chassis price difference.

Most of the Super C's will be around 34-36 feet.

The older C's built on E-series with diesels tended to be small models, because only the E-350 cutaway got the Powerstroke engine option, had GVWR almost 3000 pounds less than E-450, and a lot less payload than a gas E-350 because of the extra engine weight. BornFree sold a few on diesel E-350, Phoenix Cruiser offered as an option, and Winnebago had the diesel option for a couple of smaller floorplans in the late 1990s up to the discontinuation of the 6.0 Powerstroke.

If you are specifically talking about an E350 or E450 based C, the advantages of a diesel (if you can find one) are pretty minimal. Both the 7.3 and the 6.0 used in the E-series are detuned significantly from their pickup truck counterparts and in my opinion actually offer less performance than the V10. The exception to this would be at high elevations. I back this up from both having owned a V10 powered C, and also the fire department I work for recently switched from 7.3 diesel ambulances to V10 gas. Although the rigs are virtually identical, the V10 absolutely destroys the 7.3 in performance and at least equals the one shop queen we had with a 6.0. Now of course fuel mileage is a different story, in the ambulance application the V10 gets about 6 mpg vs. 8-9 for the 7.3.

I went from a diesel one ton with TT to a V-10 class C and I was concerned about going to a "underpowered" gasser. In the few trips I've taken so far, I have absolutely no regrets. No trouble with hills, eastern US mountains, merging onto the highway, or passing slower traffic at freeway speeds.

I am not towing anything, but I can't see how towing a small car would really affect its abilities. And, oil changes went from four gallons to six quarts!

I have had 3 Class Cs with the V10. Loved all 3. Had a DP but it was a Class A
and loved it but seldom used it. For you I say Class C MH with the V10

Diesel class C MHs are rare and hard to find, particularly used. Many you might find will have the Ford 6.0 diesel which should be avoided at all cost.
If you're going to put close to 200,000 miles on this MH then a diesel might make sense. Most people only put about 10,000 miles or less on a MH each year. It would take a long time before you ever saved much on fuel.

Well how long do you usually keep your toys?
Do you trade frequently or keep them forever like I do.
You need to know yourself before you can make that decision

I've got a 2004 Class C (Bigfoot) with the V10 Triton. It's been fine - reliable and powerful. My camper is on my F350 with Diesel but it's not a fair comparison because it's way too much truck for the weight of NL camper.

However, I can't say that I get back into my Bigfoot and feel like it's under-powered. Ford built me a great gas engine. no complaints.

Personally, I'd pick the RV I wanted for layout, size, etc. and just make sure you get enough engine for that. Fuel type would be secondary to me.

JMHO!
Bill