Well, to begin with, I use WD40 to clean electrical contacts because the lubricant protects the copper. Assuming the "best" contact cleaners provide lubrication, that's not what you'd need.
So I'd just go with the Alcohol. In fact, I wouldn't worry if it were 70%, the package should tell you all the ingredients, and "clean" alcohol should contain only alcohol and water.
Having said that, I just rub the stuff off without cleaner, I've never had bad results.