William Shakespeare's plays have traditionally been placed into three different categories: Tragedies, Comedies, and Histories. Given the extent to which Shakespeare has been studied, analyzed and critiqued, the number of categories have risen. No longer are Shakespeare's plays only categorized as comic, tragic, or historical, they have come to be categorized in seven different ways.
Comedies, Histories, Masques, Roman, Romance, Tragicomedies, and Tragedies.
As for the denoting of Shakespeare's most comical play, this defining is left to each individual reader (meaning not all readers of Shakespearean plays will agree on which play is the most comical). That being said, some readers may not even think that the traditional comedies are the most comical. For some, they may find the most humor in the tragedy plays (like Macbeth or Romeo and Juliet) based upon their inability to engage (and then finding humor in what they fail to understand or the absurdity of the story).
On a personal note, I find Much Ado About Nothing to be my favorite Shakespearean comedy.