As long as I can tell, hardware wallet has always been the safest way to store your funds offline without the fear being hacked. Some software wallet like imtoken, trust wallet and it's likes are ok too only if you store your private key or mnemonic words and keep them safe
I find that if someone is a long-term investor, use a cold wallet to store his property. As for me, most investments are short-term and medium-term, I only use the mobile wallet to hold my coin because they help to deposit coin to exchange quickly.