if you are a trader the best way to keep your assets is on a exchange. if you are using MEW import thingy I should recommend you to use metamask extension. I do usually trade in Ether Delta . Idex Coinexchange binance and Cryptopia, as a trader I am leaving my coins there for about 3 months and then do a trading. with that I can manage to double my investments and just wait .
but the best way is to store to your wallet because sometimes exchanger can scam us because they do own the control of that