I can imagine there will be more and more companies bring their cold wallet in the market. I myself have some knowledge about the hardware wallet.
1, The hardware wallet must be open-source.
2, It must have a screen to show us the tx information in case it be replaced by hackers.
3, It can not be based on an Android system, because it will bring more uncertain attacks that relate to Android itself.
4, It is better it can support multisig.

Now only three wallets can do all the things; They are
Trezor: https://trezor.io
BITHD: http://bithd.com
Ledger: https://www.ledger.com