What is the difference between potassium gluconate and chloride and which is better to take as an OTC supplement if one has repeated low potassium levels?

Weak repletion, both. If you have repeated low levels, you need prescription strength and doctors supervision. If you overuse them, being weak doses, you may overdo it. Potassium problems can cause heart rhythm problems and possibly death. Prescription generic potassium should be cheaper than otc one on mg to mg basis. This said, a gram of potassium gluconate has less potassium than a gram of potassium chloride.