an appliance with virtually no moving parts to one with lots of moving parts. My tankless had a part that started failing after a year. The problem was it wasn't a hard fail. It would work 95+ % of the time. The other 5% it would fail to produce any heat at all. You could go reset the thing, but you didn't know until you were undressed and getting into the shower.

We were finally able to diagnose the root cause and replace that part and it's been okay since.

We're remodeling our basement right now. We're probably going to go with a tankless that feeds into a tank. That will give us the efficiency of tankless and the reliability of a tank. The tank also eliminates the need to super size the tankless, and the gas line that feeds, it in the off chance that you have 5 people taking showers at the same time.

People think that the energy savings of tankless is due to not having a tank that gradually dissipates heat. That's not really true. If it were the tank would be warm to the touch. That argument becomes particularly silly for people that have recirculation lines. Those things bleed energy by design, far more than a tank. The energy savings of tankless is because of the multi-stage condensating combustion.

If I had to choose between one or the other I'd probably choose a tank. When the electricity goes out you at least still have 50 gallons of hot water banked.