The best bottom for an inground pool largely depends on personal preference and budget. Some popular options include fiberglass, concrete, and vinyl liner bottoms.
Fiberglass bottoms are low maintenance and smooth, providing a comfortable surface for swimmers. Concrete bottoms are durable and can be customized to any shape or size, but they are more expensive and can be harder to maintain in the long run. Vinyl liner bottoms are less expensive upfront and come in a variety of designs, but they can tear or puncture easily.