If you want 100% safety then I will suggest bitcoin core or paper wallet where only you have control of your keys, with other wallets your keys are accessible by wallet developers
Blockchain is actually believed widely among bitcoin users but we never know their wallets may get hacked sometimes i dont know, so it is always better not to keep a lot of coins in an online wallet like that and just keep them in a hardware wallet.
Their services got hacked few times long time ago, there's critical bug when create new address in mobile application, their services often down these days and i heard some people have problem if they activate 2FA.
Those what i mentioned already fixed, but who knows if it's still safe to keep your bitcoin there.
Also know, online methods of storing Bitcoins are actually the least safest option to do that. The core rule in saving any coins are the following : If only you have control over the private key, it is the safest option. The next question will be, " Where do you have sole control over your private key? " - Answer : Offline storage for example paper wallets and also hardware wallets like the Trezor. The main concern comes with online services managing the private key on your behalf. This is the last option you should use, if you want to manage your own money.