For Classic the default bitcoinj key derivation was used.
For HD we switched to Scrypt because we thought the algorithm was superior, and 16,384 rounds was the version used in the Scrypt description paper so we thought it was OK to use. There are various different salts used in HD so that the same wallet words used for different wallet types (Trezor walet, soft wallet) would not collide.
Thanks, that was helpful. I was surprised that not more wallets use scrypt. Bitcoin-core has some code in place to deploy scrypt in the future though.