Bitfinex might be your best choice. It's got a decent portion of the daily volume. Bittrex and Binance are also great options
Avoid Bittrex if you can help it, they are having major issues it seems, which is very bad really as they use to be one of my favorite exchange. Soething is going on there and they are not being honest about it. You can buy Zcash @ Kraken with Usd or Euro.