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
I am with this. kraken is pretty safe. even Poloniex is a bigger exchange. but they still don't have proper security. but kraken require you to verify your Identify . proof of address ID card etc. which is a good point for them.
The whole point of using bitcoin in trading or in other thing is to keep your identity hidden from the internet and if these sites require you to give identity to use them then what is the point of trading with bitcoin you can go and trade with fiat on other sites, for me the best sites to trade in are the ones that allow you short time investment and without any verification.