I have 4 water heaters in my house. They are all connected in series, meaning that the first one feeds the second, and so on.
The first one is a 50 gallon electric, with no wires connected to it. It sits in a closet right above the woodstove. There is a coil in the woodstove, and this one serves as a pre-heater only.
Next is a 40 gallon propane unit. It's about 15' from the first one. Depending on the price of propane vs. electricity, I turn it up to about 125, or off. Regardless of the price of propane, if I'm expecting guests, I'll turn it up. That way, no one gets a cold shower.
Next is a 50 gallon electric. it's right next to the propane one. It's set at 125. How much electricity it uses depends on how warm the water is from the other two.
The next one is a 6 gallon electric, located near the kitchen sink. It's about 60' from the other water heaters to the kitchen, so this way i don't have to waste a bunch of hot water waiting for it to get there.