Packaging for competitions

Being involved with the AHA and having judged national finals several times, I can tell you there are 2 concerns...first, there should be nothing on the bottle to identify it came from you. That's not too difficult. But with the number of entries we get these days, storage is a concern. The reason you should use standard 12 oz. bottles and caps is so that your beers can be stored along with all the other ones. If you use a bottle or closure that doesn't fit into a standard case, you not only screw everything up but you risk disqualification. And really, there's no advantage for you using a cork. Even if the judges saw it, they wouldn't care. For everybody's sake, stick to 12 oz. bottles with caps. If they're good enough for Westmalle, producer of the original and greatest tripel, they're good enough for us.

The rules for the National Homebrew Competition, Part I talk about bottle specs. It doesn't appear to restrict the cap type.