- Coinigy is great - they have good UI (which is saying a lot compared to other trading platforms) and you can connect it to pretty much any exchange. It is $15/month, but that's a small price to pay with the money you'll be making :) There's a free month trial if you want to give it a shot. If you don't want to pay after that, you basically have to decide between Bittrex and Poloniex. I prefer Poloniex since Bittrex has a pretty terrible UI for trading, but Poloniex has been having some major issues lately due to the increased traffic. Poloniex has the most popular cryptos and Bittrex has those plus many more.
Coinbase is there to get you started; it's easy to use and understand what you're doing. The transactions feel safe enough, and it protects you from buying too much at once. It genuinely seems like they take care of their users, especially new ones.
I have been waiting for a week now for my funds to become available on coinbase and they still are not. Plus, I have had zero feedback from the support team for a week now. Do not put your money here. Seriously.