I like using the whole peppercorns, along with dried red pepper flakes and whole mustard seeds. Brining is kind of like making stock -- you don't have to finely chop any of the aromatics. Just put them in the solution whole and don't worry about them. You'll be pulling the meat out and rinsing it anyway.
You can even put herbs in whole. Rosemary and thyme are always good for seasoning pork, so just add sprigs of each to the brine. This is very much a do-it-yourself project for people who like to come up with their own seasoning blends.