I trade with IG (ig.com). They have BTC/USD, ETH/USD and BCH/USD pairs. For BTC 7.5% margin. Spread is a little bit high at 20$, but with the high volatility in BTC it's not that bad.

Another broker I know is Plus500, they have even more crypto pairs (BTC, BCH, XRP, XMR, LTC, ETH, DSH, XEM). For BTC 3.33% margin. 18$ spread. I have never traded with them though.