Aside from the fact that using a bung entitles me to call the mouth of my carboys a bunghole
, I'd prefer to use carboy caps in every way. They're easier to get on, off, and facilitate easy, sanitary, siphoning. More than anything else, I don't have to wait for them and the inside of the carboy's mouth to dry before they'll work--rubber bungs tend to slide out if they or the carboy mouth is at all moist.
Are they sufficiently air tight, though, to prevent microorganisms from sneaking in, and to protect my brew and wine from oxidation? I know the EdWort's Apfelwein recipe mentions using them, and so, in careful fidelity to the recipe (and because the better bottle stoppers are so expensive), I've used one on the batch I have going right now. But if they're sufficient for general use--I am so tossing all my bungs!