Hardware wallets which I personally use trezor t, I've never had an issue and their interface is simplistic, one of the hands down best ways I've seen yet, but I like to diversify a bit. Anyone have issues with these? I doubt it.
If their servers go down, you won't be able to view your balance and you won't be able to create outgoing transactions.
They also know every UTXO you've ever sent or received. You couldn't develop a better way to spy on Bitcoin users if you tried.