WrestleMania 23 easily for this guy. Longest match of the Mania era (which reminds me, a big reason why I liked that they gave MITB it's own PPV, imagine how short the MITB match would've been at XXIX having to compete with Rock/Cena II, Lesnar/Trips II, & Punk/Taker). Had a great progression and the perfect balance between spots and just wrestling (for example, the WHC from this Sunday focused a little too much on the former, while the latter focused more on the latter [I think you guys get what I'm saying (and I did enjoy both by the way, so I'm in no way insulting either)]), everyone got a chance to shine in it and they had some of the best spots. I really loved Matt in that match, he was such a manipulative bastard. From him egging Jeff on to do his ladder spot on Edge (taking both out of the match) and then threatening to Twist of Fate Sharmell if Booker gets the briefcase (honestly probably my favorite spot in all of MITB). Also loved the RKO spot and Kennedy's attack on Hornswoggle (anything to beat up Hornswoggle). Finally, during the time Kennedy was my favorite guy maybe outside of Shawn Michaels so yeah, loved the winner too.
XXIV is definitely my second favorite though. Not sure about what my third is though, maybe the most recent WWE one though I haven't seen all the ones the ones from the MITB era.