No way. Best in Show is for whoever is best overall, usually best combined score between craftsmanship and performance.* Groups don't always win; skits don't always win! Best in Show at Geek-kon last year was a solo walk-on.
*I asterisk this because not all masquerades are run this way. I can't tell other people where to enter or where not to, but personally speaking? Any masquerade that doesn't factor BOTH workmanship and performance into their bests in class and best in show is cheating a lot of people out of the possibility of winning an award. You get more butthurt and less feelings of equality when a masquerade puts too much emphasis on one or the other, or puts too much emphasis on skits over walk-ons, etc. The best masquerades are well-balanced and fair to everyone no matter what skill division they are. They don't handicap singles, downgrade walk-ons as not being performance enough, and don't shove groups into their own category so they get shafted on all the good awards just because they're a group. Choose what masquerade to enter based on the fairness of their rules and how much that fairness appeals to you.
Founder and Vice-President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com