1: your parents enter US with B-1/2, you start apply I-130 and I-485 together in the US, which is faster, 1-2 years.
2:You file I-130 now. CIS will forward it to NVC after its approval, Then you need to process I-864 (affidavit of Support). then NVC will contact Guangzhou Consulate and interview your parents. must slow.
Option one is a better choice.