My personal viewpoint is that unless they were going to make John Cena the biggest heel in wrestling history by ending the streak, than Taker should've retired undefeated. A close runner-up maybe having Bray Wyatt as he is this generation's more supernatural-orientated character. But other than those two, I don't feel Taker's streak should've ended.
But if the Streak had to end at some point from 2005 to 2013 at one of his Wrestlemania matches, and with the perspective of what all of his opponents would become and what their careers and legacies turned out to be, not to mention the level his opponents were in the company at the time, the only two viable options to me are Randy Orton at Wrestlemania 21 (2005) or Shawn Michaels at Wrestlemania 25 (2009).
Of all his opponents from 2005 on, Randy Orton would go on to accomplish the most. Don't misunderstand me, I'm not talking about all time or saying that Randy Orton has accomplished more than say Triple H or Shawn Michaels. I am saying from 2005 on though, Orton accomplished the most and had the longest career. As of 2014 HBK has been retired for four years; Triple H wrestles part-time, while Randy Orton is still a major focal point in the company if not the top heel that's an active wrestler. While Orton was in a career slump in 2005 when he fought Taker, ending the streak would've been the ultimate victory for his "Legend Killer" gimmick and would've brought his career renaissance on much sooner than it did. Orton was not a guy that fizzled out or retired soon after or quit (in CM Punk's case which I'll get to later), he became bigger and bigger, which would've made a victory over Taker that much more worthwhile.
Mark Henry is an interesting choice as he would go on to become one of the best heels in the company for a number of years. However that 2-3 years away from the Taker match at Wrestlemania 22. At the time, Henry was a puzzling choice as he was still a guy stuck in the mid-card with no direction, which had been how his career had been going since the peak of the Attitude Era (say what you will about how ridiculous his storylines with Chyna and Mae Young were, at least he was a focal point and had direction as a character). So it just wasn't viable for Mark Henry to win at the time, as he was basically a mid-carder that wasn't a real threat. Having Mark Henry end the Streak out of nowhere, would've been like JBL ending the streak when he was still Bradshaw in the APA. At the time it would've been seen as a horrible choice. Now if WWE had had a Taker/Henry match in 2010/2011 right in the middle of the "Hall of Pain" era Mark Henry, then we're talking.
Batista was a huge star and one of the focal points for WWE, but he would be gone within three years of his WM match with Taker to pursue a movie career. He obviously wasn't dedicated enough to wrestling to really be worthy of ending it in my view. And before anyone tries to counter and say that Brock Lesnar did the same thing and is a part-timer now as well, exactly. I don't think Brock Lesnar should've ended the streak either.
Edge, would've been a great choice at the time. He was pretty much the top heel in the company at the time, especially on Smackdown. He was a veteran that was loyal to the company and had proven his worth. However the way fate played out, it's a good thing he didn't end the Streak. As he would be retired in three years due to neck injuries. So while Edge was a good choice, it was a good thing he didn't end it as he wouldn't have had long to capitalize on ending the streak.
Then we get to Shawn Michaels. Shawn Michaels did not need to end the streak. His legacy was already set. However, Shawn is one of the greatest wrestlers of all-time (not the greatest like WWE and many like to act, but he is definitely someone in the discussion), and if you want to go purely kayfabe, HBK was picked as the greatest wrestler in history by WWE. In theory that should mean he should be able to beat anybody, including Taker at Wrestlemania. So from a kayfabe standpoint, it would make logical sense for HBK to end the streak. Hence why he's the only other opponent in my view besides Randy Orton that I could see being a good choice to end it.
But only for their first match at Wrestlemania 25. As for the second at Wrestlemania 26, HBK wanted to retire, so clearly him losing in his last match was the right call. Because unlike Taker, HBK's Wrestlemania legacy isn't based on winning every match, it on having the best match, win or lose. So HBK didn't need to win near as much as Taker. Which would be my argument as well for the WM 25 match in why HBK shouldn't have ended. Again I don't think anyone should've ended the streak. I'm just merely playing Devil's Advocate so to speak for a few of his opponents.
As for Triple H, unlike HBK, he was not picked and hyped as the greatest wrestler of all-time, so from a kayfabe standpoint it would make complete sense for Triple H to not be able to beat Taker. From a real life standpoint, Triple H, just like HBK did not need to beat Taker. His legacy is also already set.
Last, we get to CM Punk. More than any other wrestler that he wrestled from Wrestlemania 21 on, I am so glad that CM Punk didn't end the streak. I'm a CM Punk fan for the record. I think he was the best overall wrestler in the company from about 2010 until he left earlier this year, even though WWE didn't see him as such. But CM Punk basically quit. He was tired of wrestling and didn't want to do it anymore. I don't condemn him for it or hate it. I think everyone in this world has the right to do whatever will make them feel the most fulfilled and the happiest, as long as they're not physically harming other people. I don't think CM Punk "owes the fans" anymore than what he has given. He had a great run. However, how much would it have sucked for CM Punk to be the one to end the Streak, only for him to say screw it and quit less than a year later? That would've been a huge slap in the face to Taker, Vince McMahon, WWE, and the fans. And I don't think ending the Streak would've been enough to keep CM Punk around. I don't think even main eventing Wrestlemania would've been enough. CM Punk I feel is done, at least for a good while. Whomever ends the Streak should be someone that is gonna be around for a good while and be a focal point for the company. CM Punk obviously chose that he didn't want to go that route anymore, so I'm really glad it wasn't him.
Again, I think Taker should've retired undefeated unless he lost to Cena so Cena could go on a Hollywood Hogan esque heel run, or possibly to "pass the torch" to Bray Wyatt.
But if I had to choose a Taker opponent from 2005 on to be the one to end it, I would've chosen Randy Orton at Wrestlemania 21. HBK at Wrestlemania 25 as a runner up choice.