What is the best over-the-counter antiemetic?

Several good ones. But best depends on cause of emesis: viral/bacterial gastroenteritis/food poisoning: emetrol, pepto-bismol, kaopectate; dizziness/seasickness: dramamine, (dimenhydrinate) bonine. Precautions: emetrol used with caution in diabetics; pepto causes black tongue/mouth/stools; dramamine/bonine can cause drowsiness & may exacerbate glaucoma. If in doubt, ask your fp/pediatrician.