The time to get hot water to you sink will be a little longer with tankless than with a regular tank system. Remember you are starting with cold water that has to be heated before being sent into the pipe. Reg HW heater starts with hot water.
If you want hot water when you turn on the water at the sink you need a circulating pump and a regular hot water system.
I think the instant hot water just saves you the cost of maintaining 40 gallons of hot water. But you will still have to pay for the gas to go from cold water to hot with either system.
I would go with a tank system and a circulating pump on a timer.
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