Omega Centauri will always be no. 1 for me
It was the first globular cluster I ever saw through a scope, one of the first views EVER through a scope and it absolutely blew my socks off
Then realising it was a naked eye object and could be seen through binos easily was even more exciting. I spent about half an hour when I was just starting out observing with my friend trying to track it down in a 10" Dob for myself and FINALLY got it and then I was even more excited that I was learning and could find such an amazing object!
And then seeing it in a 16"...well...
I also can't just pick one, so no. 2 for me would definitely have to be the Orion Nebula. Definitely one of those "I could just cry with joy" moment. Absolutely breathtaking and just soooo much to look at! And I even saw blues and greys in the gas with the Trapezium clearly visible. Amazing!
And third on the list is the Tarantula Nebula...after seeing that in a 16", I have NEVER forgot it. Ever. One of the most brilliant sights I have ever seen.
And Eta Carina and the nebula, holy moly, so much going on in Carina and all amazing!!!