Bancor is a decentralized exchange protocol that is designed to increase liquidity for Ethereum and EOS tokens. The company has been at the center of the debate about Decentralized vs Centralized Exchanges, as well as the overall need of institutions to serve as a hub for decentralized networks. Their protocol, and exchange, enable any token to hold one or other additional tokens in reserve. Bancor allows conversions between tokens on their decentralized exchange with smart tokens that increase liquidity, and establish market prices for smaller tokens. Specifically, for those that do not have large trading volumes. Bancor tokens facilitate the exchange and act as a connective tissue, and have a centralizing effect on the exchange.

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

UNUS SED LEO is an initiative started by Bitfinex that is focused on increasing the exchange's transparency. UNUS SED LEO means "one, but it's a lion" in Latin. The iniatative was created to increase the transparency of the exchange's finances, following a controversy related to the allocation of reserves from the stablecoin Tether, that was created by the same parent company as the Bitfinex exchange, iFinex. It is built around a token burning redemption mechanism which is tied to the parent company's revenues. Their dashboard provides insights into the fees that are collected, and the LEO tokens that are burned.