For me, 189 is right up there with UFC 100 except ATT actually won the co-main and in exciting fashion to boot. 189 didn't have a Hendo KO or Jon Jones on the under card but it did have the Thomas Almeida flying knee from Hell and rising of Gunnar Nelson.
I know there were other epic cards I'm not thinking of. What's your top pick? 
It was my favourite hands down. The atmosphere was electric.
1 PPV of all time for me.
I would agree it's the best even I've ever seen. I've watched every single one since about 62.
There was a Fight Night recently where every single fight had a finish. But once you add the notoriety of the fighters on this card, it can't be beat. 
It was the greatest I ever saw. I was saying it was the best 60$ I spent in a long time in anything and the championship fights hadn't even started. Could be prisoner of the moment but I don't think so.
The Fight Night with Henderson vs Boetsch and UFC 189 are close together for me
It was very good. Up there with UFC 84, UFC 100, UFC 139, and UFC 142
One of my favorite events, great fights top to bottom on the PPV.
I also loved UFC on VS 4, that whole card was electric! The names weren't nearly as big, neither was the buzz, but being there live...it was a distant second.
It was REALLY good. Probably in my top five. I cant say it was the best event ever though.
I liked the rory lawler fight alot. Even though it didnt go how i had hoped
It was like watching a Pride event again, so much fun!
Its easy to say number one right now, since its still so brand new.
So I'll just rate it with some foresight.
Definitely top 2 or 3 of all time
Top 5 all time fight cards.
Top 3.
Southpaw76 - I liked the rory lawler fight alot. Even though it didnt go how i had hoped
How does someone root against Robby?
Are you from Canada?
Was probably the best UFC event I've seen in a long, long time
DVandal - It was like watching a Pride event again, so much fun!It was good enough to make this man post for the first time in 7 years!
Top 3 for sure. Every time this subject comes up the first event I think of is the carwin lesnar card. Crazy fights.
BJTT_Warriormmd -.DVandal - It was like watching a Pride event again, so much fun!It was good enough to make this man post for the first time in 7 years!
Best I have seen hands down.