if you mean margin bitcoin markets, then i only know 2 markets you can use to trade the bitcoin market, that market is okcoin and bitmex. i have good experience with both but i only recommending bitmex because beside you traded bitcoin-usd, you can try trade btc-altcoin. the leverage is also legit and you can satisfied when you can place the right price. but before you try with real fund, i think you can test first with testing account in bitmex.

but if you mean only trade like usual, then you can try bittrex, poloniex, bitfinex, liqui, and else. i recommending bittrex and poloniex as that 2 sites have a large potential profit if you know trading.