Can you suggest me what bitcoin wallet is the safest? and why?
They are two types of wallet
Software wallet
Hardware wallet
If you gonna to use software wallet use block chain it provides best security to your wallet.Blockchain uses 2FA for authentication and provides more secure.
Else if you gonna use hardware wallet use trezor.Normally hardware wallet has more secure and advantages than software wallet.The hardware wallet the private keys are stored in the protected area of microcontroller so it cannot be transferred out of device as plain text.
Other than this hardware wallet provide more secure.