What the best transportation from Lowu to Causeway bay, Hongkong with luggage?

There is no bus, so you need to take the mtr.
After passing the Luohu Border, you can take the East Rail Line to reach Kowloon Tong Station and then change to Kwun Tong Line to get Yau Ma Tei Station where you can change to Tsuen Wan Line to reach Admiralty Station. The last, you need to transfer to Island Line to get to Causeway Bay.

Thank you very much Mindy.