Mexican coke tastes better because it uses slightly less sweetener and twice the amount of sodium. There’s a YouTube video by chemist George Zaidan that did a chemistry deep dive on the topic. The acidity of coke breaks down the cane sugar (sucrose) into fructose and glucose (which is the composition of HFCS). There is no difference in flavor between cane sugar and HFCS in acidic beverages, but there are often other differences in the recipes that improve taste. Most notably sodium content.