Dont get me wrong, I love CM Punk. He reminded me on Raw last week how much he's been missed due to his brilliance in the begiinings of his feud with Cena? But the best ever? He's not even the best right now at anything he does, so how could he be the best ever?
John Cena, HHH, Shawn Michaels, Hulk Hogan, Ric Flair, The Undertaker, and Sting jump right off the top of my head as stars that are or were beter then Punk. I could easily name more if I wanted to type all night.
CM Punk is very good in the ring, but his style within WWE isn't great. He's a striker with his legs and arms, and uses far too many rest holds for my liking. Unlike wrestlers such as John Cena, he can't adapt his style within the ring to have a good match with anyone. He's not a large guy, and doesn't wrestle with any type of power whatsoever. There's nothing particularly flashy about what he does either. He's a solid worker, but he's not special. Id rather see Cena's power, Angle's technical ability, or Morrison's flashy pace then Punk's striking style.
While Punk is a fantastic heel on the mic, he's not great as a face. He's had many memorable promos as a heel. His promo at Night of Champions where he went into the crowd was epic. His "Happy Birthday" promo especially and all his mic work in his feud with Rey Mysterio was both disturbing and fantastic at the same time. But his mic skills as a face are quite average, and the only one that truly stands out to me was his promo with JBL during their "drinking contest". Those with the best skills are equally strong both as hees and faces, and Punk isn't among them. Because of this, men like HHH, HBK, Cena, and Jericho are better. All of these men are equally adept at cutting promos both as heels and as faces. Punk has improved leaps and bounds to the point that I believe he could make for a solid face now, but not a main event level one.
As for the statement that Punk's never been in a boring storyline, did you miss the last few months of the SES? He was in the definition of a boring feud with Big Show, whose a pretty entertaining guy in himself. His first World Championship was rather dull as well, as he didn't have a memorable feud within it. He couldnt cut it as a face champion, and WWE realized this when the wrote him off at the foot of Randy Orton at Unforgiven 2008. Neither his matches nor the feuds during this time were any more then average. The greats tend to take any feud and make it feel special, something CM Punk has failed to do.
Its hard to picture CM Punk even on the list among the greatest wrestlers of all time. When I make that list, I would say Rock, Austin, Flair, Hogan, Cena, and HBK. The thought of adding CM Punk to the end is unfathomable. One thing he does have in his favor is that his gimmick is one that transcends the business, and is unique. His "straight edge" gimmick is one that could take him a long way, but not to the level of Cena's "Hustle Loyalty Respect", Austin's anti-authority figure, or Hogan's "Vitamins and Prayers." All of these men were the faces of their company at the time, and household names. CM Punk is neither, and hasn't been in the championship picture for almost a year. Could you imagine that happening to an Austin, Hogan, or Flair? I can't.
At the end of the day, what sets apart the greats from the rest is the epic moments they've created. Austin, Rock, Cena, Hogan, Flair, and HBK, amongst others, have created moments that will go down in history forever. And its not just been one for these men, its been many CM Punk has yet to have one truly epic moment, which seperates him once again from the all time greats. He's a tremendous performer and a star in the business, but he's not even one of the top "faces" of WWE right now. That itself makes it impossible for me to even consider him among the all time greats, let alone the greatest of all time.