It depends which region you live in. I'm in the U.S. --I trade on Bittrex, Poloniex, Kraken and Cryptopia. Bittrex so far has been great, they handled the BCC/BCH distribution almost flawlessly whereas other exchanges had hiccups, and they keep their users up to date on a consistent basis. Tickets get answered within a day or two.

I know many traders on Twitter who have had issues with Poloniex, and while there were some shady-ness going on there (delayed responses to support tickets, too much wallet maintenance, long withdraw times, etc.), I have had no issues with them. I actually submitted a support ticket the other day and received a response within 24 hours. Granted, my issue was minor.

With 2FA always enabled, Bittrex is your safest bet at the moment, but it's better to be on multiple exchanges than just one, if you can.