Preferably aluminum over carbon or graphite
Aluminum will bend while carbon and graphite sometimes break. A bent pole is alot better to land on than a razor sharp edge
Personally I don't think it is worth ever paying for a pair of poles. Its one expense you can make do with out. They don't make that big of a difference and you make go through 1-5 pairs a season. Hit up your rental shop, local dump, or lost and found