Poloniex is very annoying with this 'stopping' us from accessing our own freaking funds! I mean - if it happens once or 10 times - I understand - I cannot understand when it happens these many times!

Coinbase is the other one that is good but very very annoying as they say 'we are unavailable' just when ETH/BTC/LTC go to a point where buying or selling becomes profitable!

I like Bittrex for now (except for their wallet maintenance) - they have been consistently online! At least that has been my experience.