In the RV, we have an AC/LP water heater. We usually have electric included in our site rental.
Divide cost of Propane per gallon by 22 to get equivalent cost of electric. If propane is cheaper, then use propane. If electric is cheaper, then use electric.
Our old water heater (which sprung a tank leak so we had to replace it) was an AC/LP unit also. If you have a LP heater, then you can add either a Hott Rod or a Lightening Rod. These electrical units thread into the anode rod hole in the LP water heaters.
Lightening Rod is generally cheaper but Hott Rod is easier to find. I have seen the Lightening Rod at the local ACE Hardware.