I have used grits, polenta, and corn meal. All had fairly good results but the strength of the corn flavor varied. My favorite was the polenta. All were done as part of a decoction where I pulled off some of the thick mash and brought the grain and adjunct to a boil for at least 20 minutes.
You cannot compare these items to flaked corn which normally has already been boiled than dried. Flaked corn can be added to the mash but corn meals need to be done with a cereal mash to free the starches so that the enzymes can do their job.