8 cylinder or 10 cylinder

Hi Natalie and welcome!
I would not be too concerned about number of cylinders. It's more about the engine being able to pull the rig around.
For what it's worth, you will never be unhappy that you have too much power; are able to climb hills too easily or that cruising along is too effortless.

The Ford V10 is one of the very best engines out there for motorhomes. That is why it is so commonly used. I would not hesitate to own another one.

My V10 was in a Class C, only about 13,000 pounds, and I just loved it, smooth, powerful, and economical.

Drive both MHs. See if you are comfortable at 37 feet. Some federal, state and county campgrounds may allow 32 but not 37 feet. Such as Olympic NP. See https://www.nps.gov/olym/planyourvisit/camping.htm

V-10 hands down.

Great running motor. Won't let you down going up the grades and/or pulling a toad. She always has more power to spare.

Gotta agreed, V10 is the way to go.

Either one will work. You don't need to worry one bit about ending up with an overpowered motorhome. If you have a Ford chassis, you will almost certainly get the V10, and it's a fine engine, smooth running and reliable. The Ford V8 would get you there, too, but struggle more on the hills etc. and probably not get much if any better gas mileage or have any significant differences in maintenance expenses. (For what it's worth, the current V8 is rated about the same as the V10 is in my '98 class C.)

If you have a Chevy chassis, it's the General Motors V8, and it's also a good engine.

It probably goes without saying, but traveling alone or with another person makes rather little difference in the strain on the engine in a motorhome. Adding a few hundred pounds of weight (for the person and their clothes and belongings) to a vehicle that weights 13,000 or 14,000 pounds is barely noticeable, and the air resistance is not changed at all.

Love my 8 pistons but they are out of breath at top of hill. 10 is better. 12,000 pounds leaving drive way. Wish I had 12

Most of the time we think Class C motorhomes on 1- or 1-1/2 "ton" van chassis, like the small U-Haul "Cube Vans" and they run up to about 32 feet. Was 31 for a long time. If you're looking up toward 37 feet, it's going to be a "Super C" on a much heavier chassis or a Class A, again a different chassis.

It's not the number of cylinders, it's the piston displacement, in cubic inches, or liters, that's really the "size" of an engine.

Then there were "sizes" according to the dimensions of the engine block itself.
Ford and GM used to build "big block" V8 engines that ran from 7.4 to 8.2 liters. Those were discontinued, and now the V8's are all "small block" up to about 6.2 liters. The GM engine that competes with Ford's V10 is 6.0 liter.

The V10 is an engineering trick. Ford's largest V8 was 5.4 liters. Divide by 8 and multiply by 10 and you get 6.8 which is the V10. So it's a small block with two cylinders added, to get up toward big block displacement.

V10 is a great engine. It sounds like overkill but it isn't. On flat land, maybe. In hilly country, you want it all.

Also if you have the option when looking at used.

Go for the E450 chassis.

They come in 2 models. E350 and E450. On some of the older models it might say E-Super Duty on the fender instead of E450.

AND when you get into the long ones there is a whole lot overhang behind the rear axles. Metal fatiques and you need to look at the leaf springs.

Bring a flashlight with and get down and really check the leaf springs for cracks or broken leafs. From both sides.

I sure wouldn't dismiss the MH if one is broke/cracked they can easily be replaced by a repair shop. And can be driven safely if one is broke. AND you might be able to get it for a lower price if you point it out to the owner. He need not know that it is an easy fix either. :W

Since you are shopping used, go to a dealer and drive one of each in a newer chassis so that you know what each are capable of. Each are potent, but each have their own characteristics that you'll have to live with. Go with the one that works for you. By driving newer models, you will be able to better evaluate the condition of the one you consider purchasing.