BitFinex is a bitcoin to fiat exchange, a margin trading exchange, and a liquidity provider. The platform offers a number of features that expand the financial positions you can take - for example the ability to short Bitcoin via margin trading.
The exchange also offers a set of other cryptos apart from bitcoin such as Litecoin and Ethereum.
Deposits and withdrawals take place via the standard bank transfer means with fees of 0.1% and a minimum of $20. Bitcoin and Litecoin are free.
BitFinex takes security seriously and have moved from a hot wallet cold wallet set up to segregating customer funds where each user has access to their own wallet which they can review on the blockchain.
Bitfinex was hacked on 03 August 2016 and around 120,000 BTC were stolen.
Fee of 0.1% for most trades

Huobi is one of the world's leading trading platform, committed to providing investors with a professional, safe and honest transaction services. The Exchange charges no deposit fees but does have an exit fee of between 1% and 2%. It was originally based in China, but moved its' headquarters to Singapore, and also has offices in Hong Kong, Korea, Japan and the United States.
Huobi has raised capital from investors including Dai Zhikang, Sequoia Capital and Zhen Fund. Huobi is a major player in the Chinese blockchain scene. It runs a mining pool, (Huobi Pool) incubator, (Huobi Labs) and a research institution. (Huobi Academy of Blockchain Applications)
Trading fee of 0.2%

Bittrex is one of the largest crypto to crypto exchanges. It offers a large number of trading pairs, but do not allow fiat to crypto trading. Bittrex has one of the largest trading volumes in the market.
It is a reputable exchange with good record on security and is also fully regulated. They provide two factor authentication as well as a number of other options to secure funds. They are United States based and are fully compliant with all laws.
They support more than 190 cryptocurrencies and have a dynamic platform. It’s a good option for both advanced and beginner traders; providing advanced tools like candlestick charts and crosshairs, but with a user-friendly interface that is very intuitive.
Trading Fees: 0.25%