I have had excellent results with Noritz NRC1111 tankless.
It is one of the higher capacity models available. It also has a large heat exchanger resulting in very low pressure drop across the heater at high flow rates. Most other tankless drop significant pressure at high flow rates. Be sure to consult a gas pipe sizing chart to meet the 200K BTU gas supply requirement, and confirm the gas meter is up to the task. Also do a hardness test (Hach 5B is a good kit) and install a water softener if needed to eliminate scale build up inside the heater.
Edit: Be sure to install the optional flush valves for easy servicing.