My all time altcoin exchange is Binance.It is one of the most trusted and safe exchange.This exchange offers service to almost all coins and offers some really good price. Except this, I am also using Etherdelta sometimes which is also a exchange. You can choose one of them or both it's on you now.
Yes, I agree with you. It is better to choose the best cryptocuurrency trading site. Other people are holding some altcoin because they do not know where is the best altcoin exchange. They have many also other exchange that are waste of of your tokens. So it is better to know what is the best exchange.