Yes, Randy Orton is No. 1 on my list and I have many reasons for this. Before I start, let me just clarify that this ranking has nothing to do with all backstage news which reported Undertaker's suggestion to have Orton end the streak. Instead, I have my very own explanation and analysis for this.
Back then, Orton was the "Legend Killer." We all watched him rise with Evolution under Triple H's lead. We all saw him shock us by defeating several legends and top superstars. We all saw him become the youngest World Champion ever. We also saw how he eliminated both HHH and Edge at Survivor Series all by himself.
Orton was able to beat many superstars like Rob Van Dam, Booker T, Mick Foley, Edge and even Shawn Michaels and Triple H. Sure the latter two were able to defeat him later, but we're talking about one match here. The same could have happened to the Undertaker at WrestleMania.
Just look at the cocky smile in this photo. That is what Orton was all about, and he was playing his role perfectly. After his feud against HHH ended, Randy Orton wanted to do something big. He expressed his feelings to one of WWE's legends, "Superstar" Billy Graham. Superstar encouraged him and told him "Go where no wrestler has gone before." At the end of the segment, Orton was shown holding a copy of SmackDown magazine featuring the photo Undertaker on its cover.
I'm not exaggerating here, but as soon as I saw Undertaker's photo, my first reaction was "Oh! No! Please don't tell me he'll challenge the Undertaker and beat him!"
Orton announced that he'll challenge Undertaker at WrestleMania in a Legend vs Legend Killer match. He claimed that he would set himself apart from all other wrestlers by ending The Undertaker's undefeated streak. Yes, he mentioned the streak.
He was the first superstar to mention the streak. He was the first superstar to aim at it and put all his focus on ending it. I know it was mentioned and acknowledged in previous matches, but this was the first time in which the undefeated streak would become a major selling point for the Undertaker's matches at WrestleMania. To make things worse, he turned heel again by attacking his girlfriend, Stacy Keibler.
Some people might feel that I'm making a big deal out of this, but let me go on and explain why I thought it would end. I expected this feud to last for a while until after WrestleMania. I wasn't expecting Orton to win the whole feud and that's why I expected him to win the first match. Just like he defeated Shawn Micahaels at Unforgiven before losing to him the next night, I thought he might do this to the Undertaker.
I thought he was going to win and keep bragging how he ended the streak before Undertaker gets his revenge back. He also had his father, "Cowboy" Bob Orton on his side. As we came closer to the match, Orton became more confident about winning. He attacked Jake Roberts (a previous victim to the streak) after the latter advised him not to underestimate the Dead Man. This overconfidence was killing me and for the first time, and maybe the only time, I was too worried about the streak (I repeated this before, but it was different here).
During the match Orton showed too much confidence and his father tried to help him. As I watched, I kept wondering what would happen next until the moment I didn't want to see came. As Undertaker went for the chokeslam, Orton reversed it into an RKO out of nowhere and that is the point where I thought that the streak will finally rest in peace.
But No! Undertaker kicked out at two, and after that, I had a sigh of relief as I finally saw 'Taker winning. Orton's cockiness cost him the match later. As he tried to hit the Tombstone, Undertaker reversed it and hit the Tombstone himself.
So let's sum things up. Orton was a rising superstar who called himself the Legend Killer. He defeated some superstars who I never expected he would beat. He became the youngest World Champion. He was the first superstar to directly mention the streak and focus his intention on ending it. He was so confident that he almost made most people believe he would defeat the Phenom like he defeated others before him.
I hope I was able to convince you here. In my mind, Orton was the closest superstar to end the streak.