We recently put in a pool and had to make the same decision. We went with the concrete. Our guy puts in foot thick walls and it is a family company that has been building pools this way for three generations. The only downside I saw to concrete walls was the potential for cracking, especially up here in the northeast (I live in NH). But I went with it anyway as we did a lot of research on this guys work and were pretty impressed. Best of luck.
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