How many miles do you do expect to drive each year?
Gasoline RVs may be a better choice for occasional use, like weekend getaways..
Diesel RVs are better for high mileage trips and constant use, like for full-time RVing.
As realtors say, it's all about "Location! Location! Location!"
Will you mainly visit mountain towns and campgrounds?
Make lots of starts and stops? Drive over the speed limit? You'll burn more fuel and pay more at the pump.
Diesel engines have better fuel economy, but you'll pay more upfront for that savings.
Diesel will get you to the top of the mountain faster and more comfortable. The gas will get you to the top of the mountain, but not as fast. When you pull into the parking spot, there is no difference.
Will you be a part-time RVer? Fuel costs are affected by seasons, holidays, and fuel shortages.
There are total package tradeoffs with either, and what you end up with will be a product of all the things important to your motorhome vision.
Neither! Mileage, destination, length of ownership, and maintenance are greater influences than fuel type.