If you are completely new and want to get started with demo accounts then HitBTC is great option for you to start with. This is just for the demo one but not the real trades because this exchanger have thought to be stealing people's money, so stay away from the real trades here.
If you want to get started with the real trades then there is best option like Binance and Gate.io which can give you great head start with good user interface. For a professional trader it is very important to have the perfect UI because things should be available on screen to trade effectively. Once you gain some knowledge then you can trade on almost any exchanger out there.