All centralized exchanges come with risk, but Bittrex is one I've been using for a while without any issues (so far). I actually had my phone die yesterday, and I didn't have the 2FA backup code for that account so I was locked out. I was really impressed with their response time. I had to jump through quite a few hoops, but I got back in today. I heard a story recently of someone who's been trying to get back into their Coinbase account for over a year after losing 2FA access. Ugh!