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.
I am just storing my bitcoins in my online wallet and as of now, it is the best method that I know. I tried storing bitcoins before on exchanges but after that I moved all my bitcoins into online wallet. It is good because, I paid my credit card bills and utility bills using that wallet. Just store them wherever you want. Just keep in my mind to not share your password or pin to anyone and to always log out.