I've used about any grease you can think of, and the one thing that holds true with any of them, is if you shoot to many times they will all tend to seize. The best advice I can give you is to make sure you have some kind of grease on the threads, and after shooting two or three rounds, take your tool and break the plug loose, then retighten it, and you can shoot quite a bit without the plug being so tight that you can't remove it fairly easy.
You don't have to take the plug out, just loosen it enough to break the crud seal. After doing this, it doesn't seem to re-seal as bad. Presently I am using gorilla grease, but it doesn't really matter what kind you use, as long as it is an anti-sieze grease. Just break the seal after a couple of shots, and it will come out pretty easy when it comes time to clean up.
