Storing your BTC on an exchange is the common way most traders save their coins. But is it the best method? Cold storage to me look expensive, since it is costive to purchase hardware.
It is definitely not the safest way to store coins. Be cautious when it comes to exchanges because you are actually entrusting your coins to them. You are not the one holding or owning the private key or pin codes to your coins if you are storing them in exchange sites. A cold storage is the best but if you are only saving a single bitcoin perhaps you will have to trust some other online wallets temporarily.