My vote goes to Gatekeeper. It is by far my favorite B&M Coaster at Cedar Point. Don't get me wrong Raptor is a good ride, and Rougarou is decent... But for us Gatekeeper was the most memorable, and the one we wanted to re-ride the most. The huge lift hill, and the inversion at the top was awesome in the front row, it was really smooth, and very enjoyable. Granted it wasn't incredibly forceful, and full of airtime, but it was overall very enjoyable. Raptor was good, and very forceful, but it is not something we wanted to re-ride that day. IMO: Rougarou is by far the least impressive B&M Coaster at Cedar Point. There is nothing in the layout that really makes it stand out... It's kind of just... there. We rode it once, and had no desire to re-ride it.
Obviously these are just my opinions, and I know I am in the minority here... but Gatekeeper was by far the best B&M coaster at Cedar Point for us!! (Not to mention it looks the best in photos)