Bupa Hero VHIS Plan - Core and HSBC Voluntary Health Insurance Flexi Plan - Bronze level are both High-end VHIS plans; they differ in ward class, benefit limits, geographical coverage and premium.
Bupa Hero VHIS Plan - Core suits you better if you value a lower entry premium (about HK$10,532/yr at age 40, non-smoker). HSBC Voluntary Health Insurance Flexi Plan - Bronze level suits you better if you value 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.