...
Among the online wallets I have only used
blockchain.info. I did have a total of two issues (temporarily lost BTC) with blockchain.info, but in both cases I got them back.
blockchain.info's wallet offers an interesting feature that makes it harder for keystroke logging programs to steal your BTC: a second password
option that uses an on-screen "virtual keyboard" (a little bit like Trezor's) before you can send out BTC. You access that feature via "Settings" at the Home Page of your wallet there.
blockchain.info, of course, offers at least two Two Factor Authentication services, but I never could get them to work well. This might be especially true if you ever want to use that wallet in a developing country or with slow/bad Internet access...
* * *
But almost all of my BTC are now in cold storage on a Ledger and a Trezor.