HSBC Voluntary Health Insurance Standard Plan is the insurer's Standard VHIS plan (the regulatory floor of cover), while HSBC Voluntary Health Insurance Flexi Plan - Bronze level is its flagship Flexi plan, which extends the ward class, benefit limits and geographical coverage above that floor.
HSBC Voluntary Health Insurance Standard Plan suits you better if you value a lower entry premium (about HK$2,995/yr at age 40, non-smoker). HSBC Voluntary Health Insurance Flexi Plan - Bronze level 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.