Are concrete or steel walls better for an inground swimming pool?

Steel walls are currently the lowest quality wall for a swimming pool, with the exception of Cyprus wood (if still available).

Concrete (not gunite) is superior to any other wall, but a pool with concrete walls generally also has a concrete bottom. In other Words, it is a concrete swimming pool.

The most popular wall today for vinyl liner pools is fiberglass and, with the possible exception of concrete, is the best possible choice.