If you are "comfortable" on your bike, I would say take the sportbike class. Each day the class is divided into beginner, amateur, and advanced groups. You can specify which one you would like to start in and move to another if you feel the need. The non-sportbike day is the more of the "cruisers" (HDs, Vulcans, etc.) and may be frustrating for you because you have the potential to take the corners (and straits) faster and someone may always be in front of you with you riding their butt trying to get around them. You're not learning that way.
From talking to others in the class (and seeing what they are riding), if you have any skill at all, you probably want the sport bike day. There are even guys with KLRs an V-Stroms that come on this day.