In this moment Xapo is safest one
I'm considering them as the safest but I'm a practical person. Their fees are even higher than electrum which is also a good wallet but if I'm going to choose, I would prefer the cheapest one and that is blockchain.info. They are also trusted and one of the most popular web wallet that I can trust with but I'm not going to let all my bitcoins stay there.
Who os Electrum wallet owner? Trust for trust i Will trust on Trezor and Mycellium to spend however once again you Will need a paper wallet that could BE Stolled, wiped in water floods or burned in fires or destroyed um hurricanes or earthquakes...
Xapo owner is a well know entrepeneur in silicone valey and one of PayPal directors. We dont own the private keys but know to who we are trusting it.
Well its expensive but Security have a price. I never heard before about Electrum wallet to have bunkers spread around different continents to store 85% of coins on coldstorage and a satéllite to do surveillance to website.