I know there are a lot of wallets available.
This is why I want to know your opinion what is the best online Bitcoin wallet, in level of security, protection of our Bitcoins and availability of support.
With all due respect to you OP, there are already threads like this in the past. If you truly wants to seek it you can search for it.
There's no web wallet to be considered as best wallet in terms of "protecting bitcoins" like you stated as one of your criteria of choosing. All web wallets have chance of becoming a fraud one but it doesn't mean they can't be trusted.
Just use some of them for a purpose like when saving transaction fees or by means of converting coins.
In terms of support availability, I see Coinbase and XAPO has fast response since I already send queries to them many times.