Bittrex is one of the quality exchanges where there is a large selection of altcoins. The support service responds at a normal speed basically. As for security, too, nothing bad can not say. I often trade on Bittrex and everything suits me.
I can't agree with you about support service. I wrote to the bittrex support many times and some of my questions were answered after weeks. The same bad support work I saw on poloniex.