I've used Bitfinex and Bittrex. Both about the same really, but very different to Coinbase's usability - you can set stops, limits, market rates etc. You may need existing cyrptocurrencies to trade into certain coins - not all currencies have EUR/USD as a trading pair.
I find it easiest to buy either ETH or LTC on Coinbase [much lower fees than BTC], transfer that over to the exchange and then you can trade from that.