I'm not sure what my favorite Mania is, but I'll at least address my thoughts on each Mania stated thus far . . .
WrestleMania XIX ~ Definitely one of my favorite. It has by far the best Rock/Austin match in my opinion; Lesnar vs. Angle is perhaps the greatest closing match in Mania history, and one of my all-time favorite Mania bouts; Shawn/Jericho, while I find it to be highly overrated, is still an extremely good bout; and pretty much every bout was at least average. I really didn't enjoy the handicap match from memory, and I've never been able to will myself to actually sit through Hogan vs. Vince. So those two things, particularly the latter, stop me from out-right saying it's my favorite Mania.
WrestleMania XXVIII ~ Entered the show with the thought that this was going to end up my favorite Mania, but didn't leave with that impression. I know the positive effects it had, but still judging the Mania solely on the content it provides (and the build to it), Bryan vs. Sheamus still sucks and I was really looking forward to it. Rhodes vs. Show should've been the quick squash match, as it would've made sense from a narrative perspective as the whole build revolved around Show's embarrassing Mania moments. HHH vs. Taker was amazing, five stars match in my opinion. Jericho/Punk was a disappointment, especially since I've been dreaming about them main eventing a Mania for the WWE/World Heavyweight Championship since their first bout happened in 08, but it was still a really great match. Loved the story they told. Rock/Cena didn't disappoint, it was exactly what I expected. An average match filled with false finishes. Considering the competitors, I'm not sure why people expected a five star match, or anything better than that but meh. I was satisfied with it. The twelve man tag match sucked, especially the ending. Eve betrayed Team Teddy, she should've taken her Team Teddy shirt off after kicking Ryder in the nuts. I was highly disappointed that she remained fully clothed. Nothing else on this show merits a comment. The Mania was all right, certainly had fun watching it, and probably one of the better ones I've ever seen.
WrestleMania III ~ A one match show for me. Steamboat/Savage is definitely one of my favorite matches to come from a Mania, maybe even in wrestling but that's literally where my praise ends. Most of the matches were too short to leave any kind of an impression unless it sucked like that midget match. The main event with Hogan vs. Andre was dreadful to watch as well.
WrestleMania X8 ~ I uh, only saw RVD vs. Regal & DDP vs. Christian. I know, I should totally get around to this one.
WrestleMania X-Seven ~ Haven't seen a lot of this PPV but I don't think it'd rank from what I've seen. Benoit vs. Angle, was absolutely incredible. Jericho vs. Regal was decent. Didn't really like Taker vs. Triple H. Austin vs. Rock is very overrated in my opinion, and I'm bored during the middle of the match every single time I've watched it. For me, it's an average bout at best. And the TLC match, while entertaining, wasn't nearly as good as their triangle ladder match the year prior and it wasn't even as good as their SummerSlam TLC match in my opinion.
WrestleMania 13 ~ Only watched the Submission match, which is definitely my favorite Stone Cold match, but I still find it very overrated.