WM17 will go down as the best for one match only - Kurt Angle v Chris Benoit. That is the greatest piece of technical wrestling you will EVER see. The other big matches like Rock/Austin II and TLCII just cement its place. Shane v Vince was fantastic as well.
My top 5 (in no particular order)
WM17
WM22 (HBK/Vince and MOTN Foley/Edge steal the show. Cena/HHH one of the best main events in a while. The only dent in it was Rey/Orton/Angle and Booker/Boogeyman. Mickie and Trish put on one of the best women's matches you'll see)
WM8 (very underrated in my opinion. Hart/Piper is one of the greatest midcard WM matches of all time. Flair/Savage was epic, Jake Roberts v Taker another standout battle)
WM4 (not because of any really great quality matches, but because it cemented how important of an event Wrestlemania is - a one night, 14 man tournament for the WWF championship - Randy Savage wrestling 4 times in one night to capture the gold was a great story - defeating the likes of Butch Reed, Greg "The Hammer" Valentine, The One Man Gang, and lastly - the greatest man in the WWE never to (legitimately) capture the big one - the "Million Dollar Man" Ted DiBiase. The event also marked Bret Hart's face turn in the opening battle royal by destroying the trophy won by Bad News Brown (RIP) after being double-crossed by the master of the ghetto blaster)
WM3 (Steamboat/Savage stole the show. Hogan/Andre was the main attraction with the slam heard around the world. Biggest crowd in WM history. The often forgotten 6 man match between the British Bulldogs and Tito Santana vs the team of Dangerous Danny Davis and The Hart Foundation didn't disappoint either)
On a side note - some of the greatest single matches in WM history (on a not so great card) that are worth checking out
WM7 - "Retirement Match" between the "Macho King" Randy Savage v The Ultimate douchebag, i mean Warrior. Probably the best match in the history of Warrior's career.
WM13 - "I Quit" match - Bret "The Hitman" Hart v "Stone Cold" Steve Austin - the match where the crowd turned on both men. Austin was no longer a hated heel and Hart was no longer a beloved face. 50mins of an absolute classic. The only disappointment was Shamrock being the special referee.
WM21 - Kurt Angle v Shawn Michaels - stole the show of WM21 in what arguably was the feud of that year. Anytime these two were involved in a match it was automatically an instant classic
WM19 - Shawn Michaels v Chris Jericho - great back and forth match, with Jericho putting the exclamation mark at the end.
WM10 - Bret Hart v Owen Hart, no matter what anyone says, this is the best opening WM match of all time.