As stated above, one thing to consider, if you are considering propane? Propane generators use a LOT of propane. From everything I've read, they will drain a 30 gallon propane tank in your RV, like .... within hours.
Personally, I have not found any application where I wished my generators were propane instead of gas. I suppose if I somehow wired them directly to run as a whole house generator, that would be different, only for convenience and the need to refill the gas every 16 hours.
This is something you should really ask yourself before purchasing.... When, why, how often, and under what conditions would you use propane to power your portable generator instead of using gasoline? And ... how readily available and convenient will it be when your generator runs out of propane to refill it?
HOWEVER! On the other side of the coin ... it is nice to have options ... gas or propane? Because you just never know!