May I know the best and faster way from Shantou to Guangzhou?

As for your demand, I have to suggestions for you:
1. take a shuttle bus from the downtown to Chaoshan High-speed Train Station. It will take you into Guangzhou in around 3 hours. You can search for the timetable of the trains on the train page in this website. U'd better book the rail ticket in advance. Btw, the fare is CNY164 for a second class seat and CNY207 for a first class seat.
2. U can go to ST Coach Passenger Transport Central Station to take a direct bus to Guangzhou. It takes 5-6h and the bus fare is CNY150. It would be fine to buy a ticket on the spot.