What's wrong with potassium chloride? I've been using lite salt (50/50 sodium chloride and potassium chloride) in my diet to help make sure I get enough potassium, and your comment has me a little concerned.
The citrate and bicarbonate forms are much better tolerated, and at much higher doses. I take 3 teaspoons a day of potassium citrate, in water, spread throughout the day (I built up to this over time) because I have a mostly meat and dairy diet. This yields approximately 6 grams of potassium a day. For most people building up to 2 teaspoons a day is sufficient. This much potassium chloride would be dangerous.
The primary symptom of too much of the citrate or bicarbonate forms is diarrhea. Also, the metabolic byproduct of citrate is bicarbonate, which has a far greater effect on body pH than taking bicarbonate itself, as the process increases blood pH rather than that of the intestinal tract.