I've found coinbase is pretty easy to use and there's less verification required before you can buy crypto currency but the downside is they only offer 3 coins-Bitcoin, Ethereum, and Litecoin. I think they're adding Bitcoin cash in January.

I use Kraken and Bittrex to buy other coins that aren't offered on coinbase. If you're going to be on Steemit I'd recommend getting a Bittrex account as they're one of the few exchanges that offer STEEM. You can increase your steem power by buying STEEM and transferring it to your steem wallet through Bittrex as well. I've done this a couple of times and it's increased the value of my upvote.

Hopefully you find what you're looking for in an exchange. Like I said, I have accounts on Coinbase, Kraken, and Bittrex and I use them for different purposes. Check them out and decide which ones are for you and good luck!