Closing... you ?
For me, opening.
Tough call, but I'd go with opening. I find those are more spectacular (although the parade of nations can become a bit tiring to watch after a while).
... the exception would be if Celtic Woman or one of it's former members was performing at the Closing ceremony.
Would you rather see:
1. Lisa Lambe is a movie-musical of The Bloody Irish,
2. Susan McFadden in a movie-musical of Legally Blonde,
3. Alex Sharpe in a movie-musical of Beauty and the Beast, or
4. Amy Rivard in a feature-length Candy Canadiana movie.