I think, to even suggest that CM Punk is the best of all time is ridiculous. You're entitled to your own opinions and all that, but man... Now, if we're talking who is CURRENTLY the best in the world, in terms of active wrestlers in the industry right at this moment, than I have to give it to CM Punk. But of all time? No way.
For me it's got to be the perfect mix of in-ring work, promo skills, marketability, look, etc etc. When I say the "best in the world" or the "best of all time" it's gotta be the PERFECT storm. My biggest issue is just how ambiguous this question is...
Currently, CM Punk is the best active professional wrestler and sports entertainer in the world. I would make a case for John Cena based on popularity and marketability, as well as influence, but as this is a personal decision I also have to weigh his in-ring ability, which I don't enjoy at all. The only thing Punk MIGHT be lacking is size, but that's easily solved by just partnering him up with the right opponents. The industry isn't flooded with giants and body-builders anymore; it's getting easier and easier to find guys Punk's size to put on great matches. Punk has got the total package, and while I currently enjoy Austin Aries more, Punk's sheer range and platform that the WWE allows him gives him a huge edge.
Now, best of all time..?
I'll get this out of the way: I don't like Hulk Hogan, and I'm not going to consider John Cena because it's a can of worms I don't want to devolve into right now. This is a highly personal and preferential discussion, so of course it's just going to come down to MY standards. There's only so much objectivity you can have...
I'm going to throw a couple names out there: Kurt Angle, Eddie Guerrero, Shawn Michaels, Triple H, Bret Hart, Steve Austin and the Rock. With the possible exception of Bret, all of these guys possessed the "perfect storm" i was just talking about. And again, Bret is debatable because I lot of people will say his mic work was damn good from time to time. He was certainly a good enough worker in that ring to make you forget that he lacked in ANY area.
Eddie goes off the list first, even though he's my personal favorite. He WAS passion, and he breathed his chracter in every single facet of his performance. Some guys cut good promos or have a great look. Eddie took his charisma, developed this perfect character, and then played that out into everythign from his promos to his facial experessions and body language. Eddie Guerrero, for lack of a better term, WAS Eddie Guerrero. But he was also on top of his game for too short a period before his tragic passing. He's done less than all the guys I mentioned, and therefor doesn't make the cut.
Next to be cut is Bret Hart. It almost pains me because of how damn good he was in the ring, but the Screwjob really did fuck with his career, and once he went to WCW I had no interest in watching him. He was also arguably the worst promo of the guys I've listed.
Between the five remaining (Angle, HBK, HHH, Austin and Rock) I have a very hard time progressing further. I can make case after case for all of them. Angle would likely be the next to get cut, but he's simply good at everything. His Olympic wins gave him a character and sense of legitimacy, much like Lesnar's UFC reign makes him scarier today. He's one of the all-time best in the ring, and he's cut some of my favorite promos and done some of my favorite feuds. He's easy to love, and easy to hate.
HHH is my all-time favorite heel. Promo work, ring general, one of the best looks in the industry. The guy was, and still very much is, a machine. Evolution was my all-time favorite faction for a very long time, in no small part to Triple H. Despite people's ignorant hatred of him, he's also done more to put over young talent than almost every top guy in the company put together.
HBK is over-rated, but still damn good. He's one of my least favorite promo guys today, but in his prime and given the right guy to work with he was easy money for the company. I'd probably cut him next though, because while he's well-known for stealing a show and providing some of the biggest industry moments, he sometimes lacked a weekly consistency that some of the others had more often than not.
Austin, Rock, HHH or Angle. I honestly have no idea... I'm sure others have their own idea, but I go back and forth between these guys all the time.