In my opinion, these exchanges are good.
Coinbase:
The most renowned cryptocurrency exchange in the US, Coinbase, has fully secured various altcoin choices. It comes with a rudimentary user interface perfect for rookies and very high liquidity. Although it may have high fees without the premium version, and users may not have access to wallet key control, the wallets are custodial and insured.

Cash App:
Cash App is a money transfer system that allows exchanges between peers, like Zelle or Venmo, while having the aptitude of withdrawing Bitcoin or cryptocurrency to individual wallets. Not to mention, the simplistic user interface works well for beginners. Keep in mind that 3% of the currency charged during transfer through a linked credit card. Investment in stocks, ETFs, and cryptocurrency made as well.

Binance:
Offering lower fees than other most used exchanges, Binance is the optimal choice when it comes to altcoin trading. It currently holds the ranking for the most trading space done globally, causing a good amount of trading exchanges taking place on a daily basis.