Personally I like both for different reasons.
At the Openings everything is all shiny and new and exciting ready for another season, the clubs are busy but nicely busy, the weather is great and you get a really good crowd of people.
Closings are good cos the end of the season is coming to a close so everyone is partying to the full, however at times the clubs are unbearably busy for some of the main closings and the weather is generally not as good.
I like to do both, if I could only do one I think Closings would edge it only for the fact that if you do Openings then that's it for the season.