A gunite pool is made of concrete and sprayed onto rebar frames.
This type of pool is structurally the best, will last the longest verses the other 2 options of pools and can be customized to the homeowners needs/taste.
Fiberglass pools are large molds approx. 1inch in thickness installed into the ground. They are already a certain shape and size, which may limit if they can fit into your backyard space. These require rip out and replacements every 15-25 years because there is currently no industry to repair this in NJ. Fiberglass pools are also vulnerable to certain soil conditions and ground water.
Vinyl Pools area rigid aluminum frame that a liner gets installed into. This pool has the same installation process as an above ground pool except they have supports that go into the ground. With this type of pool, a liner must be replaced approximately every 7 years.