I found that coinbase and coinbase pro has worked well for me. I've used others like binance,  bitfinex, crex24, bittrex,stex, and a few other main ones.
I feel secure using coinbase. Fees are high on coinbase but it's a start for anyone new to crypto. Beat way to do it is, deposit money into coinbase and then transfer it to coinbase pro to trade/buy coins and go from there. Fees are much lower in coinbase pro.
As well I havent heard or seen any types of threats or hacks on coinbase.