I've never been to Carlisle, but I can comment on the Nats, Vegas, and Spring Fling.
The NATS have 3000+ show cars, huge drag racing, huge swap area, the cruise on Brice Road, and the off-site burnout contest.
Vegas has about 200 show cars, lots of drag racing, a good size swap area, and it is in Vegas. The best thing about the Vegas show are the cruises from Phoenix, LA, San Fran, Utah and Canada.
Spring Fling is 400-500 show cars, agood size swap area, and it is in LA.
IMO the best show by far (again, I've never been to Carlisle) is the Nats. But the single best thing about any of these shows is the cruise to Vegas. I love seeing the cars at the shows, but seeing 100 vintage and modern Moapr musclecars cruise from Phoenix to Vegas is the best.