It is one of the best as its open sourced with features with two factor authentication, no one would able to access your coins. Compared to coinbase, which have full access of your coins, blockchain.info do not have unencrypted private keys which means a hacker who can hack into blockchain.info online wallet would possibly never get your BTC. The best online desktop would still be Bitcoin Core, you would be getting the fullest control over your private key as no one else have access to your private key regardless of whether it's encrypted. Blockchain.info still have control over your encrypted private key but it would be hard to brute force. For the best online wallet with best security, blockchain.info would be recommended.