Rheem tankless gas water heaters: Probably the best choice if you want a hassle-free instant water heater that will give you hot water whenever you want without needing a repair every other day and one that does not take a fortune to install.
100 Gal. Tall 3 Year 399,900 BTU Ultra-Low NOx Natural Gas Commercial Water Heater
Noritz NRC111-SV NG Indoor/Outdoor Condensing Tankless Natural Gas Water Heater, 8.4 GPM. Details at http://youzones.com/noritz-nrc111-sv-ng-indooroutdoor-condensing-tankless-natural-gas-water-heater-8-4-gpm/