I'm almost ashamed to have voted Lesnar considering some of the arguments and voices coming out of that camp in this thread.
The reason I'm voting for Lesnar is quite simply because of the context. I think X's post was the most fair one out of all that I've seen. I much prefer The Rock to watch in all aspects, he's probably in my top 3 guys ever, but people are being far too quick to undersell Brock here just because he isn't considered one of the best of all time. There is one category in which Lesnar trumps the Rock, if only just about but still. That category is booking.
In the quest of getting Lesnar over first time around they threw to him Hlk Hogan (who had not long ago taken the absolute top guy, The Rock, to the limit at Wrestlemania), The Rock, as feverishly discussed already in this thread, The goddamned Undertaker. He got the best of everyone he faced until he turned face against Big Show. That was the first time he'd been pinned, almost a year in. Then he won the royal rumble, and then beat Angle at Wrestlemania. Arguably, the only guy to really get the better of Lesnar during his whole first stint (asides from Eddie Guerrero who he never really feuded with, and only lost the title to interference) was Goldberg himself, and only then because both guys were on the way out and they wanted the face to go over.
Then he returns and kicks the crap out of the face of the company for 25 minutes before getting beaten by two moves. That could count as a mark against but you thinking people know and I know, that Cena beating him in the fashion he did, and in their first encounter since him returning was just the flat out wrong decision. He should have been booked to win in a story that could've ran until Summerslam. Instead they dropped it after one PPV and seemingly killed his momentum almost instantaneously. Despite this, he would go on to feud with HHH. Break his arm, not once but twice in the course of their feud, and beat him two out of three times over the next year. He got the better of HHH in a feud. HHH. The guy that overbooked himself so much, he beat CM Punk during the hottest angle in years in 2011 despite Punk beating Cena clean only months previously and despite only being a part time wrestler.
He was/is so highly booked, he doesn't only not wrestle on free TV, he only wrestles about four matches a year,only at the big PPVs. Now, this is also true of The Rock granted, and The Rock defeated CM Punk after the longest title reign in the last 25 years. That's massive. He also beat John Cena AT Wrestlemania. That's arguably bigger. That's be like if Hogan had beaten The Rock in Toronto at WM 18 and The Rock had gotten the win back the following year. Of course that didn't happen, because unlike for Cena the vast majority of fans like The Rock despite the smarky Canadian crowd, and were on his side again by the end of the match.
But Brock Lesnar ended The Streak. That's unfathomable. A feat so great it can only ever be done once and Lesnar was the man to do it. In kayfabe, that trumps anything the Rock did whilst he was back. Just ask the crowd seconds after it had happened.
Factor into all this that Lesnar has been booked in a similar vein in this very tournament. People have thought it fit to put him, right or wrong, over Hulk Hogan and HHH. One all time great, and one in the very next bracket of greats. The Rock has had no easy road here either, it's not possible to get an easy road this far, but Lesnar's was harder. Going over Sting is an unappreciatedly difficult task. That man got to the final a few years back and is a regularly semi-finalist in this tournament. But those two guys are too similar. Both known for being meteoric faces, and in that situation The Rock is always going to win because in last '99 and 2000 he was untouchable as a face.
What I'm trying to say in a very long-winded way is... If this is a one off match and I'm asked to vote, I go with The Rock 99 times out of 100. He's just more entertaining, more of a star, he can carry a show better, and in his prime, go the distance in the ring just as well. But the way WWE view his value to them by winning and being a monster, the way the voting has gone in this tournament has made Lesnar winning this match the likely option, not the surprise one. If beating two of the toughest opponents of all time doesn't matter up until this point then there is veritably no point in the context of matches. But Lesnar did, he's beaten the toughest guys to get to this point, and that puts him in good stead to beat another. It's all about context. Brock Lesnar is an absolute freak of nature physically. He can actually fuck someone up in a real fight and he uses a portion of that power and ability in the ring to wrestle. After beating the absolute best guy that there is (Hogan), you'll have to excuse me if I don't see why he should lose to number 2 or 3. Rock beating Lesnar would be expected normally if you're talking about the greatest. But given the context of this match, it would be inconsistent booking. After his run, Lesnar should go to the final and fight an opponent he's never fought and a guy some people would say is the number 1 guy, and that'll be an apt way to determine the winner this year. Lesnar v. Austin, the match everybody wanted to see.
Whoever wins, though, fantastic match. One of the closest and most hotly contested semi-finals I can remember from this tournament.