We visited Mount Eden for the New Year’s Eve countdown. Even though it was crowded, the summit is spacious enough that you can always find your own spot to enjoy the view. However, keep in mind that the distance to the Sky Tower is quite significant, so the fireworks might look smaller than expected.
Pro Tip: Don’t rush to leave immediately after the countdown ends. Traffic can be a nightmare as the narrow streets get clogged with cars. Unless you are sure you aren’t blocked in, it’s better to stay and enjoy the night for a while longer.