jimbo is correct. With electric, nearly 100% of energy goes into heating the water. Actually, 100% does go into heating the water, but then some of that is lost to the outside.
With gas, you have to take the price per therm, figure out the cost per BTU, take into account how much goes up the flue, and then see what the equivalent rate is. Most people assume that gas will always be cheaper, but that is not always the case. Around here, the operating costs would be similar, but having gas would have an additional service cost, so unless other things in the house were also gas, that service cost would wipe out any savings.
In addition, electric units are much easier to install and have other advantages. No vent pipe, no gas line, no worries on getting combustion air, no worries about combustion gases leaking into the home, no worries about gas leaks, etc. Because of this, you have more options as to where you could place the WH as well.
Gas has a faster recovery, but that is just due to the size of the burner. You could get the same in an electric model, but the electrical load would be too much for most homes and the wiring to the WH would have to be increased to meet this load.
Overall, electric would be safer, but there is nothing wrong with gas as long as the install is proper. If your friend has other things that run on gas, then there is no reason not to use a gas WH (assuming that gas is really cheaper and the gas line/vent are already in place). If the WH is the only gas device, then your friend would be better off by dumping the gas WH and going electric unless electric was much more expensive than gas.
An additional advantage for electric is the operating costs are more stable. Natural gas prices can swing up and down much more than the cost of electricity. Serveral years back, natural gas was at record lows. A bunch of companies built a bunch of natural gas plants for making electricity. These plants can be built small and quickly and they thought they were getting a great buy. Of course, they were using the record low gas costs to figure operating costs and did not take into account the historically large swing in prices that gas goes through. Well, by the time they got them built (or before), gas went back up in price and the utilities couldn't afford to operate these plants except to cover peak loads. So, what I am saying is that even if gas is cheaper now, you should look back and see what prices have been in your area and think about what the prices might do in the future. When the price of gas is low, there is a good chance that it'll shoot back up.