I've seen different types of otc laxatives (stimulant, saline, stool softeners, etc.). which would be best for occasional treatment of constipation?

If occasional: it doesn't matter much what you take, but it sounds like you have a number of GI issues. The best way to treat constipation is to avoid it, but taking in adequate fluid and a good amount of fiber, preferably from natural sources (like fruits/vegetables with lots of roughage). Stimulant laxatives can lead to dependency, and I generally recommend avoiding them. Occasionaf milk of magnesia (magnesium hydroxide) is ok.