If you really want to to day trading, their are differents exchanges you can use.

It depend what you want really, if you want to try on the new coins that may do a X4 X10 X20 then i will advice Cryptopia exchange or coinexchange.io .

You can also use Yobit or coinnova, but there are lot of pump and dump and scam coin there.

If you want to trade middle to high market coin, you can use Bittrex or Poloniex.

I myself do new coins to middle old coin. I dont choose the coin that are already in the top 100 of COINMARKETCAP.

More the coin is new highest the reward can be, but the risk is also really high.

Im mixing invest and i dont invest all in the same coin.