"Safe" is a very interesting word. It really depends on what you are trying to protect yourself from.
In many cases it might be "safest" to trust someone else to secure your bitcoins for you if you aren't capable of taking the proper steps to securing your own bitcoins. In that case, the "safest" might be something like Coinbase. They will handle the process of storing multiple backups in secure locations and insuring their assets. Unfortunately, since they have full control of the bitcoins, there is always the possibility that they run off with them or are hacked.
If you are going to store your own bitcoins, then there are a few risks you need to be aware of and to protect yourself from:
- Risk that your wallet will be lost or destroyed (fire, flood, earthquake, tornado, lightning, volcano, tsunami, hurricane, mudslide, vehicle crash, hard drive head crash, etc).
- Risk that a hacker will access your wallet through the internet
- Risk that a stranger will physically access your wallet (breaking&entering, physical theft, etc)
- Risk that a friend or family member will access your wallet
- Risk that the a government agency will seize your wallet
- Risk that a criminal will resort to extortion, kidnapping, or physical threat to get you to send them your bitcoins
Some of these can be protected against with any wallet simply by making sure that you maintain multiple recent backups in secure locations.
Some of these can be protected against with any wallet simply by making sure that you use a very strong password.
Some of these can only be protected against with BOTH a very strong password AND maintaining multiple recent backups in secure locations no matter what wallet you use.
Some of these can only be protected against by making sure that nobody knows that you own the bitcoins, no matter what wallet you use.
The only thing you are protecting against by choosing a "safest wallet" is the ability for a hacker to access your wallet through the internet. In this case, any wallet that is not connected to the internet is equally secure. Therefore, if that is what you are trying to protect yourself from, you can choose any of the following:
- Properly created paper wallet
- Armory offline (requires a computer that is never connected to the internet)
- Electrum offline (requires a computer that is never connected to the internet)
