Which is best travel from Guangzhou Zhongshangba station to Dongguan.

You can take local subway line 5 at Zhongshan Ba to GZ Railway Station. There you can take a fast train to Dongguan. The metro fare is CNY2 and the rail ticket fare is CNY45.5 and CNY50.5, respectively for a second class seat and a first class seat.

I know there is Three-day Pass for GZ metro, at the cost of CNY50. U can take local metro lines for unlimited times within 72h since the first use with it. And there is also One Day Pass, which costs CNY20 and is valid within 24h. After using, you can take the cards in private, not refundable. Apart from them, Yang Cheng Tong shall be a good choice for you. It can be used on metro, buses, ferries and taxis.