We plan on a tankless for the house we might build someday, and maybe a second tankless for the radiant heating system.
Our six gallon oem water heater operates so well and stores the hot water we make so long, I can't imagine a tankless accruing enough benefits to be worth trying.
We have hot water in under 20 minutes, have never run out, and leave it off all day unless we are going to use it. Water remains hot eight to twelve hours.
Not instantaneous, but pretty great.