Who's Better at Speed Ball?

The photo shows the latest best times for each block in speed ball.

F and B are Math 6+ and E, A, and C are Math 6.  All of the Math 6 classes are faster than the Math 6+ classes!  But does this mean that Math 6 is better at speed ball?  Can you tell which class is actually the best?

Here are the number of students in each class:

F: 24 students

B: 24 students

E: 19 students

A: 19 students

C: 19 students

Use unit rates to prove which class is actually the best at speed ball.