The Ledger Nano S is the latest generation hardware wallet available from Ledger. There are many differences in the security architecture, the firmware and the available features.
Ledger Nano S has a screen and two buttons. Everything is done directly on the device: PIN entry, seed configuration, transaction validation. There is no need for an additional security card like for the Nano or HW.1.
Furthermore, Ledger Nano S can manage multiple applications such as Bitcoin, Ethereum or FIDO U2F (strong authentication).