I went tankless three years ago. I did a ton of research, including examining a variety of installed units, and I went with a Noritz...which is made in Japan. Noritz is a very high end unit. They are not cheap. I buy American whenever possible, but it is undeniable that the Japanese are the acknowledged leaders in tankless designs. Thats all the Japanese use. they make them by the millions.
after 3 years, I would never go back to a tank. My unit is so efficient that I was able to (legally) use 4" Schedule 40 PVC for the exhaust. That's how little heat is wasted out of the exhaust! Further, my burner draws combustion air from outside, so no waste of interior air and no flow through air leaks to waste energy.
Benefits: substantial energy savings, especially if you have a bigger family who take a lot of showers...PROVIDING you can get them to turn off the hot water!
Never run out of hot water.
Adjustable hot water temps.
Unit is substantially smaller than a tank.
Things you must accommodate: no electricity = no hot water. Battery backup strongly advised.
My unit has a 200,000 BTU burner (yes...200k!) That means a 3/4 gas line no more than 30ft. From meter and with no more than five 90 degree bends.
Installation is not simple, but it is well within a competent homeowner's ability.
Every time you turn on the hot water, the unit runs. Get used to that, or locate the unit where you can't hear it cycle.
Freezing temps require special behaviors if the outside temp goes below -15 F.
Yes, it is advised to drain the heat exchanger yearly...just like it is advised to drain your water tank every year. I takes less than five minutes to do that procedure on a tankless - there are only a few ounces of water in the exchanger.
Check out Noritz high efficiency tankless units. They are among the best in the world, IMO