Which is the best exchange platform to use ??
It all depends on your region, the coins you are interested in, etc...
I personally am using Binance, Kucoin and CoinExchange. The last one, cause it has new coins faster and these can grow a lot when they hit Binance.
I also have an accoint on Cryptopia, but never used it, and I am verifying my account at Kraken, to convert it again to Fiat money.