I'm already familiar with coinbase and Gdax but they only cover four coins at the moment.
What is a good exchange where I could buy and sell alt coins like Ripple, Dash, Monero, and Cardano?
Ideally, the fees will be zero or very low. Obviously I want something secure as well.
Etheredelta has many tokens, but's it's definitely not user-friendly. It's hard to understand. Bittrex is a good one with a simple interface, try it. You can also go for Binance which is also a trusted exchange.
ED just got a DNS hack too. Best to let that settle down first.