We were constantly replacing our three hot water heaters due to the caustic water in Midland. Despite precautions of drip pans and water alarms, it seemed we were always having leaks. So, we replaced the units with tankless water heaters.
Although the units are "energy efficient" don't expect a quick return on your investment. Your energy savings will only amount to about $75 a year and at that rate it will take almost 1/4 century to pay for the upgrade. Beware that your house could require more than one unit or a larger whole house system to accomodate clothes washing and showering at the same time. Additionally, it is suggested that you install a water softener and have the tankless heater flushed out once a year. (This requires a service call.)
While I love the fact that I don't come home to find water leaking on my hardwood floors any more, I don't like it that the water takes so long to heat and make it to the faucet. If I understand correctly, a little water has to run through the tankless unit so it can register the temperature of the water. Then it turns on to heat it. Since there is no stored water, you just have to let the water run until it warms up. In the winter this takes about two minutes and probably about one minute in the summer.
The shower runs at 4 gallons a minute and the sink about 2 gallons a minute. Start extrapolating those figures to other household appliances and multiply them by the number of times a day that you use each water source and it amounts to quite a bit of wasted water. We may be saving energy, but we are surely wasting water. Is the trade off worth it?