The worst WrestleMania, I believe beyond a shadow of doubt, was WrestleMania X. I'm one of the rare people who actually loved WWF from 1993-1996, but this was just senseless, atrocious booking, especially for a WrestleMania, and it's tenth anniversary for that matter.
First of all, Bret Hart in two matches? Why? Why even make it so that Bret has to face Owen on the top of the card? They could have had him face Yokozuna in the main event, get Owen to attack him post-match and then give them their match at King of the Ring. But thanks to the shitty idea to have both Hart and Luger win the Rumble, Yoko and Bret both wrestled two matches on the card.
Then the God awful matches that were Savage vs. Crush, M.O.M. vs. The Quebecers, Earthquake vs. Adam Bomb, and Bam Bam & Luna vs. Doink & Dink. First and foremost, Savage had no business watering himself down to face some random mid-card performer in the form of Crush, a match with little inspiration and pay-off for Savage. Had Crush won, things would have been much different for him, but that wasn't the case. Then waste Bam Bam's ability on this equally meaningless match, and you've put two potential main eventers to waste. They could have gone with Bam Bam vs. Macho Man if they wanted at least one more good match on this card, worth paying to see.
Earthquake vs. Adam sounds like a good idea for a big man match on the surface, but those plans went south. Plus you got two superheavyweight brawlers versus two small technicians in another waste of card space.
I'll admit that Blayze vs. Kai for the women's title was a pretty good female match, one of the only good women's match ever on WrestleMania, and of course you had the legendary Razor vs. Michaels ladder match, so those two provided some goodness in the midst of mediocrity.
As for the best, I'll agree with WrestleMania X-Seven. Rock vs. Austin swerve was magnificent, Taker vs. Trips is a showstealer, we got TLC II, Kurt vs. Benoit was as good as advertised, and how can you hate Jericho vs. Regal? It was no show stealer, but you can't say it was bad by any stretch.