A combo of both?! I like to do a combination of exchanges and hot/cold storage.  In order to increase my liquidity and access to the market at all times, i like to spread coins across multiple exchanges and limit the amount I keep in each one, reducing my risk exposure.  Large majority of coins should be held in a secure hardwallet like trezor or nano ledger.  Furthermore, temp storage of ERC-20 tokens on meta, myetherwallet can create flexibility and liquidity along with the integration of hardwallet verification