Blockchain.info is the most commonly used one.
Blockchain.info is the most popular one but I do not think it's most secure. Have a look at its history:
https://hn.algolia.com/?query=blockchain.info&sort=byPopularity&prefix&page=0&dateRange=all&type=storyI have been using xapo.com - I think it is great you can make more then one wallet and put 2 auth on one wallet and make the other wallet a hot wallet.
It has no fees to sending to other xapo members (which is great since faucet sites will pay instantly to xapo members)
I have not had any problems
Do you mean there are even no bitcoin transaction fees?