vCore Medical Plan is the insurer's Standard VHIS plan (the regulatory floor of cover), while vBooster Medical Plan is its flagship Flexi plan, which extends the ward class, benefit limits and geographical coverage above that floor.
vCore Medical Plan suits you better if you value a lower entry premium (about HK$3,265/yr at age 40, non-smoker). vBooster Medical Plan suits you better if you value a higher annual benefit limit (HK$8,000,000).
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.