Personally using xapo wallet and I am satisfied. But I think that blockchain.info one of the most good web wallets as u can get private keys from your wallet (in xapo I can't).
After blockchain.info changed to HD version, we can't see the private key. I think we must use many web wallet to save our bitcoin. No one web wallet guarantee that our bitcoin is full secure. Always get news update about the best recommended web wallet from bitcoin.org.
All web wallets are secured based on their technical aspects but of course in our own preferences, we are not to take those securities of them to take care of our coins.
The primarily used of web wallets in my case is just to use their service since no doubt they have some services that can bring convenient to the customers. But I will exclude blockchain.info to that since they are primarily for bitcoin storage services purposes. And now that you guys mentioned that we aren't able to hold our own private keys then it's no sense at all to use that web wallet.