Not sure when it comes to your region - I'm in KY, and we went with steel. Here you can choose between a full gunnite pool (no liner), steel walls (vinyl liner), plastic composite walls (vinyl liner), stainless steel walls (concrete bottom - no liner), or fiberglass walls (liner or concrete bottom).

Whatever you choose, don't let the warranty play much into the decision. The warranty will typically only cover the wall itself, and not any labor associated with actually replacing it. You can buy an entire set of steel walls for my pool (18x38 grecian) for less than $2000 at the time we built the pool. I'd say a single replacement wall would be in the hundreds. The labor on the other hand would run in the thousands, with the very likely need to replace the liner after the repair - adding another $3000 or so.

I'd go with steel (galvanized of course) and you'd probably be fine.