Welcome to the forum
There are a lot of diesel/gas discussions on the forum, so make sure to search around for the many ideas and opinions about both.
From my perspective... and not exhaustive...
. Great for smaller class c units (sufficient power, easy to maintain)
. Lower cost of maintenance and easy to find service
. Familiarity (similar to gas car engine)
. Somewhat lighter in weight
. Note that any generator will be gas or propane
. Lower relative cost than diesel
. Lower life span (although doubt that will be an issue with RV miles driven)
. Less power (must run at higher RPMs to get most torque)
. Torque is typically significantly less
. Towing tends to be more limited due to less power
. Great for large class c units (more torque at lower RPMs)
. Will outlast the class c (like energizer bunny, keeps going and going...)
. More reliable through greater ranges of hard usage and towing
. Sounds "manly" -
. Any generator will typically be diesel
. Higher cost of maintenance and slightly harder to find available service
. Heavier than gas engine
. Harder to start in cold weather (generally, starting is a little different)
. Must use DEF fluid for emissions
. Higher cost than gas (can be more than $10k greater)
. Will get about the same gas mileage and gas costs about the same
. Have about the same noise level, although different "voicing"
Bottom line is it all depends upon the use. When the engine is paired up correctly for the intended usage, they both can serve well. Basically they are just different and meant to serve different purposes.
I love 'em both, but my gas engine is 707 HP in a Hellcat and my diesel is 1250 ft-lb of torque in a class a DP.