So I'm gonna breakdown the cards mainly cause I'm bored and I've rewatched these fairly recently
WMXX
Cena/Show - Pretty meh, was cool seeing Cena go over and win his first title but Show was ass during this time and Cena wasn't what he would become yet.
World Tag Titles - A mess, not a fan of this concept at all, felt like they were just trying to fit everyone on the show and this match wasn't any good either
Christian/Jericho - Real good stuff here, can't say anything bad about this one, nice swerve ending as well
Evolution/Rock and Sock - More good stuff, great seeing Rock in the ring again and the match itself was also good and not just bc of the novelty of Rock being back
Evening Gown match - I mean this sucked but like ass and titties so I won't really complain
Cruserweight Open - Again they just wanted to get everyone on the show and this was fine for what it was but holy shit I didn't need this many <2 minute cruiserweight matches, would have preferred a fatal 4-way a million times over
Goldberg/Lesnar - LOL glad they made up for this years later
WWE Tag Titles - Ugh another one, isn't any better than the Raw match
Victoria/Molly - Build was fun, this match wasn't, they just rushed it to shave a woman's head.
Eddie/Angle - Really like this one, they have better matches but this one still rules to me
Undertaker/Kane - Glad this only got 8 minutes bc these two never have good matches together, Bearer's return was the only real highlight
Triple Threat main event - Obviously awesome and it's what makes people love this show so much, great fucking match and Eddie/Benoit celebrating afterwards with JR's commentary might be better than anything on 21, but it can't eclipse the rest of the card.
WM21
Rey/Eddie - Solid opener, a little disappointing bc they've had way better matches but I still fuck with this only bc it was an opener
MITB - First one ever and it fucking rules, I always like most MITB matches and this first one did great setting the standard that may have only been beaten a few times in the many MITB matches we've had since
'Taker/Orton - One of the first good streak matches, not amazing by any means but it had it's moments that delivered and then some like that Chokeslam counter into an RKO
Trish/Christy - fucking sucked
Angle/Michaels - Just rewatched this earlier today (s/o Adam Cole) and HOLY SHIT it is so amazing, one of the best matches in 'Mania history easily
Sumo match - LOL glad this was short
Cena/JBL - Kinda sucks, these two didn't have the best chemistry unless they were beating the absolute shit out of each other like the "I Quit" match they'd have later
HHH/Batista - Amazing build-up but also a little disappointing too, not a bad match by any means but they also end up having way better ones later in the feud.
So I still say 21 easily from that just from it's consistency even with it having lackluster main events compared to XX bc XX just has too much shit in between the 4 good matches on the card. Quality > quantity wins here for me, but I'm also not trying to shit on XX by any means bc I like it a lot too, I just think a lot of you guys are looking on it with some crazy rose colored glasses bc of the good matches on it where 21 was good all around and didn't have near as much filler, but the title matches not being as good definitely hurt it.
EDIT: Also these two were tied in seeding points so I'm not surprised at all how close this is but they're up against X-Seven next