Which card is the best for us when traveling in HK?

During our trip we arrive on HK airport 18. of nov, then going to our hotel (Xi hotel), next day 19. of nov. exploring HK and leaving 20 of nov. to Guangzhou by train. Then arriving 15. of dec back in HK at the airport, going back to Xi Hotel and leaving HK the 16. of dec. at 23.45, so that day we will also explore the city. Which transportation card is the best for us?