Bitmex is currently the largest Bitcoin exchange according to BTC volume. You can short bitcoin or go long with their top-of-the-line margin trading system. Coins available for trading on Bitmex are: Bitcoin, Cardano, Bitcoin Cash, EOS Token, Ethereum, Litecoin, and Ripple. Deposits are only available with BTC.
Bitmex has a quality referral system and a VERY informative blog.
No USA citizens allowed, although KYC is very minimal.