The answer to 'tankless vs tank water heater which is better' is that tankless water heaters are generally considered more energy-efficient and cost-effective in the long run compared to traditional tank water heaters. Tankless models heat water on demand, only using energy when you need hot water, whereas tank heaters constantly maintain a full tank of hot water, even when not in use.
Tankless water heaters also take up less space, last longer (often 20+ years), and provide a continuous supply of hot water. However, they have a higher upfront cost and may require electrical or gas system upgrades for installation. Tank water heaters are typically less expensive to purchase and install, but have higher ongoing energy costs and a shorter lifespan of 8-12 years on average.