Would I be wrong to relate your question about the best cryptocurrency trading platform to the best cryptocurrency exchanges because most cryptocurrency trading are carried out on exchanges my personal favorite would be binance
Its okay. When we say trading platform that is pointing out to those exchanges so there's nothing wrong with it. And I think this thread is already full of good suggestion and as you can see most of them are telling that binance is a good choice.
And for saying what is the best exchange, this also depends on the experience of each trader here. For "decentralized" exchange which we solely believe it is, IDEX is a good one for me and I did several trades there so if you are for ERC20 tokens you can use that exchange.