1.Vitamin C is more natural compared to the trademarked or patented Ester-C.
2.Vitamin C is L-ascorbic acid while Ester-C is mainly calcium ascorbate with vitamin C salts.
3.Vitamin C is more acidic than Ester-C.
4.Vitamin C is cheaper than Ester-C.
5.Although still highly debatable, Ester-C is originally said to be more bioavailable than vitamin C.