You're going to need more than one in all honesty.
-Coinbase has the best UI, it's good for researching coins even if they aren't available on there. (I recommend linking it to your PayPal account if you have one)
-KuCoin for the coins that you can't get on Coinbase
Coinbase for the most part doesn't list just anything, so if you want to put some money in something that's super early and not available on mainstream exchanges, you will need a crypto wallet (ie: TrustWallet, MetaMask or Coinbase Wallet)... not gonna lie, it's more of a learning curve and it seems intimidating initially, but that's because we're still extremely early with all of this.
Blockchain tech is literally where the Internet was in the late 90s/early 00s and it's not slowing down or going anywhere.