I've found Kaopectate usually works best for me as it treats many different symptoms, including diarrhea. I've found it eliminates gas, cramping, and stomach aches. I used to take Imodium and then I would have to take Pepcid to calm my stomach. Pepcid takes a while to work, but Kaopectate works on me in about 15 minutes. It has the same active ingredient as Pepto-Bismol but doesn't taste chalky (I take the Kao caplets and swallow them with water).
The only side effect I have noticed is that it causes constipation if it's taken in higher amounts, so I try to stick to 2 caplets.