Through research and experience, I'll try and help you make an informed decision as what to replace your ailing water heater with, or not. Fuel gas, whether natural gas or propane, electricity, as well as combustion by products are extremely dangerous. This article should never be construed as an instruction manual to install a water heater, which if improperly performed can result in minor to serious injury, death and property damage. Any water heater install should be left to an experienced and qualified service person for evaluation and installation. Your life and those of others depend on it. Perform any repairs or choose equipment at your own risk. There are exceptions to every rule. If you have a wood burner outside, solar cells, or even wind or hydro electricity with some sort of Rube Goldberg setup, these "rules" may not apply to you. If you like heating water outside on an open fire or just love cold showers, these will not apply to you. Having your own nuclear power plant means that you probably don't live in a mobile home, so this will also not apply to you either.
If you have a dedicated closet for your water heater that is only accessible from a door outside, this means that you will need what is called an atmospheric water heater. This isn't unlike a unit in a conventional stick built home, but the main difference being that the cold water line is at bottom side. Although you might be able to physically install a regular home water heater, my advice is don't. These can be either in gas or electric, with the main determining factor being what you already have installed; I'll go into this further in a bit.
If you happen to live in a double wide like mine, or the water heater is accessible from inside your home, then your options got a lot more limited, and expensive. Since these water heaters must draw combustion air from underneath and not the side, an atmospheric water heater will NOT work safely, if at all. The best case scenario is that you'll have it in a sealed closet and it will run out of air because the water heater is covering the air intake. Worst case scenario is that you snuff yourself and your family out. So your choices are either a direct vent mobile home water heater, which has a sealed off exhaust and intake, or an electric water heater made for mobile homes. I'm not going to even entertain tankless units, indoor or outdoor, because these are expensive to buy, expensive to retrofit, and expensive and complicated to maintain and service. Outdoor tankless (and tank ones) water heaters need freeze protection in case the power or fuel source fails. Indoor tankless units need a complicated vent structure that would need to run through your living space in a mobile home. Even if you happen to have this by an outside wall, you're still going to have to upgrade your plumbing and electrical to some degree to get one to operate. Many are not yet certified to be installed in a mobile home. With their astronomical price of install and maintenance coupled with the inherent depreciation of a mobile home, these are not a wise investment. The small amount you save on your gas or electric bill will be more than eclipsed by the costs to install and use it. Much like a hybrid or electric car, your heater would have to last over 20 years to realize any real savings. Most last 10 to 12 years, which is comparable to a conventional storage tank water heater that costs less than half as much. If you own and are happy with your purchase of such technology, this article does not apply to you. It's unlikely you're living in a mobile home.
So let's say you come to your senses and want a tank water heater. It's going to be a combination of infrastructure, cost and how much you want to get into to replace one. Electric water heaters are simple to maintain, and do not burn fuel so they are inherently safer than a gas one. However, you do have to have at least 100 amp service and if you already have an electric dryer, range and an air-conditioning unit, your panel may already be at its limits. My advice is that if you already have the infrastructure, replace your water heater with the same fuel type. I changed an electric to a gas water heater in 1997 on my old house and it wasn't too bad moneywise, but it took me six hours and a lot of pissing and moaning to get all the plumbing right. This was in a stick built home. If I did this same repair today, it would likely cost me 3 times as much. The assessment is that it isn't worth it to convert in either time or money.
In most parts of the United States, natural gas is cheaper to use than electricity for heating anything. Even something as exotic as a heat pump water heater is going to be triple or more of the price of a gas or electric one (remember depreciation) Truth be told, if the conditions are not right, the electric heating elements will be on a lot anyway. The extra money you spend on a gas over an electric will be recouped in a year due to lower utility bills. Although propane is more expensive than natural gas, it's still far cheaper to heat with that than with electricity. Again, your pocketbook as well as the expected life of the equipment, the costs to maintain it and not just the first cost, must ALL be taken into consideration when selecting equipment to heat your water. In the case of a mobile home, your life as well as your insurance coverage depends on making the correct choice. My advice is to choose wisely. Maranatha!