I have been using Coinbase with absolutely no issues, CEX.io is a UK based exchange that's supposed to be really good too. And lastly, Coinspot has been super easy to use. You can even buy alt's direct without going into BTC. I've heard a lot of bad press about Polo in the last few weeks. Not sure if you were aware of the BTC split that created BCH? But Polo held onto everyone's money they were entitled to until the value dropped significantly and Polo users watched a great opportunity run away. Not sure whether it was due to poor development, or bad management, but either way, Poloniex caused their own customers a great deal of stress!