There is no "safest" altcoin in this world. Every altcoin has their own risk and you have to face it anyway. It's not about how to rid that risk but how to minimize that risk as possible. Try to read and don't even try to following other recommendation because it would be bad if you were lose.
I believe such coin is Ethereum. It will bring more and more traction all over the year, and it will make him much more sustainable.