i like kraken, there is leverage there and other features, bitfinex also seems good, but there was an hacking attempt in the past, the one that is still somehow safe is only kraken to me
Indeed, kraken is quite good when it comes to their services yeah go for this exchange platform, But in bitfinex I doubt, as we all know before it has a big controversial issues. And the damage that it gave is not a joke to their investors.
Bitfinex is now regaining the trust from their clients and now they succeed. As you can see from the data here
http://coinmarketcap.com/currencies/volume/24-hour/ bitfinex is now in the first rank of bitcoin marketplace with over $10,479,800 traded within a day. I can say that bitfinex is still being trusted by their users even after they're getting hacked recently and losing millions of dollar.
You might doubt about the services they have offered because of the hack but, people still want to trust them, I'm myself never use bitfinex but just amazed of how they could regain their trust.