I'm not going to my friend's show.
Why wouldn't you go to your friend's show?
I'm going to a party that night and it is a bad show.
You should reconsider going to the show. Even if it is a bad show and you miss the party, you might hurt your friend's feelings if you don't go and show your support.
I have fun more partying so I should go to the party.
I understand that going to a party might be more fun, but your friend's feelings are more important. Nurturing your friendship and showing report is more valuable in the grand scheme of things.