Depends on the application, like me asking WHICH car is best?
My Mercedes is a fast and takes turns like a rocket 0-60 in under 6 seconds BUT no way would I take that car out in the Snow for that Subaru Rules
Certain applications you may need high volume for short periods tanks are the way to go.
Prolonged usage at a given flow tankless coils are the best
Tankless coils generally are more efficient as you have less stand by losses and coils last a heck of a lot longer then a tank.
With a tankless coil set up with a boiler you can fine tune the system for the best of both worlds.
Again you need to know the system requirements.
On some of my larger installations I have used 4- 200 gallon tanks in parallel and on other high rise residential buildings I used a coil that went through a boiler with a firing rate of 2,520,000 BTU input per hr just to meet peak demands.
18 GPH # 2 oil Or 2,100 CU FT Natural gas as it is a duel burner.
I can just about run an 11/4 line fully open 24 -7 and not run out the way this piping arrangement is designed with the tempering valves and other add ons to make for a professional installation.
Know your system needs then you can decide your exact requirements.
Basic Fixture unit demand works wonders