The answer to 'which is better tankless water heater or tank water heater' is that tankless water heaters are generally more energy-efficient and cost-effective in the long run, but tank water heaters may be a better fit for some homes. Tankless water heaters heat water on demand, only using energy when you need hot water, while tank water heaters keep a reservoir of hot water ready at all times, which can be less efficient.
Tankless water heaters take up less space, have a longer lifespan, and provide a continuous supply of hot water. However, they can have higher upfront costs and may require electrical or gas upgrades to your home. Tank water heaters are less expensive to install but have higher energy costs and a shorter lifespan. The best option depends on your home's hot water needs, available space, and budget.