hi everyone i want help for trading which exchange is best for trading on mobile and low fees 
Not everything is traded on all exchanges. You need to check on which exchanges the coin you are interested in are traded (you can use this website to search for the coin https://coinmarketcap.com/). And then you can choose the exchange available for your coin on "Markets" tab.
It basically depends on where your choice coin is been graded. Thus you might ended up having accounts in almost all tradition platforms..... In ranking though, I would recommend Bittrex, Poloniex, Yobit, HitBTC, Krakken, CoinExchange and Cryptopia.