Is Nexium and Dexilant (dexlansoprazole) the same or what is the difference which one is better?

Almost same but not. Both pills belong to antacid category Proton Pump Inhibitors(PPI) and decrease gastric acid production. They are used for treating common GERD symptoms , esophagitis, ulcer disease etc. some people tolerate one medicine better than other, for most part they can be considered equivalent however should not be used without discussing your current meds and potential side effects with your doctor.