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Bittrex is my preferred exchange. I've yet to encounter any hiccup or downtime. Poloniex on the other had seems to have issues almost daily. They lock withdrawl/deposits for alt-coins frequently, beyond simple wallet cleaning requirements. I also had issues with Poloniex losing my withdraws. I had to harass their customer service half a dozen times for a resolution to which they still never responded. Customer service is complete garbage.

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