While I don't have a lot of confidence in Poloniex - their acquisition by Circle makes them an interesting player in this space in the future. Circle's been a huge player with institutional crypto investors already and the addition of Poloniex gives it signficant consumer scale now. They're also coming out with Circle Invest - a Robinhood/Square-like app which allows for easy household trading of crypto. Jointly, the volume of investments processed through Circle/Poloniex now shoots them into the top 5 I think.

Both of course have had their share of scandals, hacks, and DDoS attacks so buyer beware still. But - it's hard to argue with that scale and the level of innovation we're seeing out of Circle. They may be a major platform player before long.