I have had two Takagi natural gas water heaters in the past. They were very energy efficient but more problematic than a standard tank unit. They waste more water, there's a longer delay to get hot water. Also I don't like the "cold water sandwich" effect. For example you get in the shower after using hot water else where, the shower water starts off hot from previous usage, then it goes cold for a bit before the tankless kicks back on. If you have hard water or on a well, I would not recommend one as the mineral build up will cause it to plug it up quickly. They recommend descaling and flushing out once a year, this will require a flush kit. I would not recommend any type of electric unit, natural gas or propane only.