AIA Voluntary Health Insurance Standard Scheme is the insurer's Standard VHIS plan (the regulatory floor of cover), while AIA Voluntary Health Insurance Prime Scheme is its flagship Flexi plan, which extends the ward class, benefit limits and geographical coverage above that floor.
AIA Voluntary Health Insurance Prime Scheme's ward class depends on where you are hospitalised — HK / Macau / Mainland: Semi-Private Room; Rest of Asia: Standard Private Room; Outside Asia (emergency): Standard Private Room.
AIA Voluntary Health Insurance Standard Scheme suits you better if you value a lower entry premium (about HK$2,846/yr at age 40, non-smoker). AIA Voluntary Health Insurance Prime Scheme suits you better if you value a higher annual benefit limit (HK$5,000,000) and a stated lifetime benefit cap (HK$20,000,000).
Neither plan is categorically better — your choice should rest on your own budget, where you expect to seek treatment and your family needs, ideally after a financial needs analysis.