It depends on the wallet type you are using. 'Hot' wallets can be hacked into easily, since private keys is not stored safely. Hackers can get your data through phishing mechanisms, or you don't act carefully while using the Internet.

'Cold' wallet is more secure, as it stores your private keys online.

So, in a word, when choosing between the types of wallets - ‘hot’ and ‘cold’ - the cold one is certainly more.In terms of particular wallets, there is a range of reliable models out there.

Here are just a few exanples: Bitcoin Core, BitGo, BlockChain, Trezor, Ledger Nano S.Yet, of course, not all wallets will suit your needs in equal measure. Plus, some of them, although secure, lack a convenient interface.

In case you may be interested, you can check you the project I am working. It is a cryptowallet that tries to marry convenience with security, while also ensuring user’s anonymity - https://www.diamondguard.io/