AIA Voluntary Health Insurance Prime Scheme and Chubb VHIS - Superb Plan are both High-end VHIS plans; they differ in ward class, benefit limits, geographical coverage and premium.
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 Prime Scheme suits you better if you value a stated lifetime benefit cap (HK$20,000,000). Chubb VHIS - Superb Plan suits you better if you value a higher annual benefit limit (HK$6,000,000) and a lower entry premium (about HK$11,581/yr at age 40, non-smoker).
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.