The answer
Storage tanks last 8–12 years due to corrosion after anode depletion. Tankless units last 20+ years with regular descaling. DOE reports tankless systems are 24%–34% more energy-efficient for homes using <=41 gal/day by eliminating standby loss. Switching is ideal for space savings and continuous supply, but may require gas line upsizing or heavy-gauge 240V circuits.
Sources
This answer is drawn from the standards and guidance below. It is general information about how these systems work — not a diagnosis of your property.