Poloniex allows users to trade over 70 cryptocurrencies (in exchange for other cryptocurrencies) on their trading platform, compared to just 3 cryptos offered by Coinbase.
Offers far lower trading fees than Coinbase (although Coinbase users can use GDAX to save on fees).
Cons
Website loads slowly, compared to other cryptocurrency exchange sites.
Customer service leaves a lot to be desired.
Private key management is centralized, exposing funds to custodial risks.
No advanced order types.
Does not accept fiat currency.
Was hacked in 2014. However, the exchange fully refunded the affected users.
Requires users to create accounts and verify their identity for high-volume activity.