The anode rod is a sacrificial thing. It is purposefully made to deteriorate instead of the steel tank. This happens irregardless of gas or electric. It has to do as much with the mineral contents in the water as much as anything.
Only Suburban water heaters feature an anode rod. The anode equalizes aggressive water action, providing cathodic protection for the tank. It is a very important factor in tank life and should only be removed for inspection, draining or replacement. It is removeable using a 1-1/16" thin wall socket.
All Suburban water heaters are protected by a magnesium or aluminum anode to prolong the life of the tank. Under normal use, the anode rod will deteriorate. Because of this, we recommend it be replaced annually or when consumption or weight loss of the rod is greater than 75%. Note: Water with high levels of iron and/or sulfate will increase the rate of deterioration. To extend anode life, drain water from tank whenever the RV is not being used. Avoid any extended time of non-use with water in the tank.
Another consideration is if you have or are hooked up to 30 amp power supplies.
I took this from the FAQ section. It is about the Suburban but is also applicable to the Atwood water heater if equipped.
Suburban's electric switch and much more
Around the 2002 model year and later, the Suburban water heater came stock with a 1440 watt electric heating element. What this means is it will take 12 amps to power it with 120 volts, when the element is on and heating the water. You may need to keep this in mind when hooked up to 30 amp power supplies, as it may cause breaker(s) to trip if you exceed the maximum amount of amps on a circuit. You may need to turn the electric heating element off... if using other high amp 120 volt appliances at the same time, like microwave, air-conditioning, coffee pots, hair-dryer, etc.....as you would only have 18 amps available to power these other things. (30 amps total minus 12 amps for the heating element = 18 amps available)
In other words 40% of your available power is going to the electric heating element when using 30 amp RV's/power supplies...... but only when the heating element is actually energized and heating the water.
I think best and preferred methods are highly subjective. What works best for your particular situation should be the preferred method. If I camp in the hotter weather down here in the deep south, my air conditioner runs a lot. I have a daughter who will not use a bath house, and is going to run the hair dryer (another 12 amps +). So if she takes a shower, then turns on the hair dryer upon exit...there is no way 30 amps can power all of that, and the electric heating element which will be on now heating the new water, since she just took a shower.
That's when I just use propane, as we need an A/C more than an electric heating element. Same thing goes if we are trying to use the microwave, and air conditioner...and someone in our group is showering. My RV can heat up quickly without an air conditioner.
Now when we're camping in cooler temps and no need for an air conditioner, I run my water heater off of the electric heating element, with absolutely no problem.