I am going to say 2001, followed by 2000, 1991 and 1998.
2001 was the 2nd best Rumble match, IMO (after ‘92) - what made it s good was the pacing. A build up which actually suggested a handful of potential winners, rather than the usual obvious one or two, and each of these entered fairly spaced out - Kane #5, the Rock #13, and Austin, Rikishi and Undertaker all in the final few. The ending was a surprise (even though Kane was presented as an potential winner, I’m sure most were surprised when the final 3 were him, Austin and the Rock and yet HE made the final two. Add to this the fact the overall card was stacked, with the Dudleys v Edge and Christian for the tag titles, a brilliant ladder match between Chris’ Jericho and Benoit, and a decent WWE Title match between Kurt Angle and Triple H, and you have a near perfect Royal Rumble card in what is probably WWE’s best ever 18 month period, creatively and in-ring.
2000 has perhaps the greatest Royal Rumble undercard in history (the beginnings of the Dudleys and Hardy Boys epic feud in a tables match, the best streetfight in WWE history between Cactus Jack and Triple H) but is let down by that Mae Young moment and a mediocre Rumble match with few high spots.
1991 was a very good card, nearly took my top spot, with a fantastic tag team opener (Rockers v Orient Express, find it on the Network if you haven’t seen it, and remember when you are watching that it took place in 199-freaking-1!), a decent secondary tag match between Ted DiBiase/Virgil and Dusty/Dustin Rhodes - Dusty’s last proper WWE match and also a brilliantly executed and super hot babyface turn in the post match angle; a WWE title change and a strong Royal Rumble match where the booking actually made most of the participants come out stronger than when they went in (something very few Rumble matches achieve) but the title match wasn’t brilliant, and whilst the Boss Man and Barbarian has a better than expected scrap, it was still the Boss Man v the Barbarian so there’s only so much they can do.
My final ‘semi finalist’ is 1998, as I love the Rumble match, and the casket match for the WWE title is decent, especially when you realise Shawn Michaels broke his back half way through but still finished the match. Vader v Goldust was also a strong opener. However, the Mexican minis ‘comedy’ match and a poor tag title match (New Age Outlaws v the Legion of Doom) let this show down slightly, plus I’m just not a fan of the casket match gimmick, no matter how hard Michael’s and the Taker worked.
So for me, that’s the final four of ‘best overall Royal Rumble card’, with 2001 taking the plaudits.