The one on the 21st is a smaller competition. Less teams, less people. ("Nationals" for cheerleading is a misleading term...there are many, many national competition...)
High school comp was in february, college was in january. UCA all-stars (big big comp) is mar 10-13, americheer (smaller) is the weekend of the 21st. And then there will be the Cheerleading World's April 22-23 (hosted at Disney's "milk house"), and they are the "best of the best" so there are less teams, less people.
I think that's it for Disney comps.