In this moment Xapo is safest one as you can see here :

They save more the 85% of coins in cold storage in swiss military bunkers splitted on different continents. Means your private key will be splitted too for different continents.
As seen here :

https://qz.com/1103310/photos-the-secret-swiss-mountain-bunker-where-millionaires-stash-their-bitcoins/

If Governement, police or thiefes comes to your house they can stole your printed cold storage private keys  and in Xapo this is too much harder to happen . So physicly Xapo security is much higher and online is similar or pretty higher because regarding website Xapo rented a methereological Satelitte and  is using it as alarm to check if website is under silent attack one day ...

Well that said, the disadvantages of Xapos are only for those whose those Bitcoins are not clan or the money they are using to upload Xapo to buy Bitcoins is from suspicious source or if you dont identify your self on  properlyand honest way,trying to openning different accounts  with fake ids and things like that  then they can seize your freeze your account until you identify your self clearly and honestly!