Yeah for me it has to be Wrestlemania 24.
It was just a great show overall. Almost every match had great importance and were big time matches. HBK vs Flair was a good story, despite of what some might think of the match. Batista vs Umaga was poor, but at least it felt like it was some important match. The divas tag team was decent, but at least it showed Santino Marella and Snoop Dogg. We crowned a new ECW Champion in Kane, in a match that lasted 9 seconds, thankfully. Big Show vs Floyd Mayweather was a draw, and the match was actually pulled off quite well.
The WWE Championship triple threat match was very good and underrated by many. Plus, nobody at all expected Randy Orton to retain. The money in the bank ladder match was awesome as always with great spots and a shocking victor in CM Punk. The Finlay/JBL match was decent and hardcore. And the Undertaker vs Edge match was good but extremely overrated. I was entertained from the start of the show to the very end, and that's all that really counts.
And that is why this was the best show of the year.