This is an easy one for me. I've been watching every match in the tournament again, which is why I've been slow to get my comments up for some rounds. It's partially to refresh my memory on the matches so I can make a clear, unbiased decision. It's also due to the fact that @Kirbi hasn't seen a bunch of the matches, due to not being a fan for quite as long, so we're watching them back so she can take part. But despite going back to watch the matches again, this is the one round where I cast my vote before giving the matches a rewatch. I knew there was only going to be one winner.
I voted for Hart/Austin. Not only was it the better match here, it arguably deserves to win this entire tournament in my opinion. Fantastic work by two performers in their prime.
The psychology of the match was brilliant. Both guys were 100% in character at all times, from the moment they entered the arena. The brawling looked very intense and real, and that's something that is often done wrong. Agreed with Tom about Bret's brawling. It's exceptional. He has a reputation for being a great technical guy, but Bret could brawl with the best of them. He was a true all rounder.
There weren't as many big spots as in some modern matches, but there didn't have to be because every move was done to perfection and sold to perfection. Everything seemed more authentic here, from the brawling to the chair shots, to something as simple as a superplex.
Bret zoning in on the knee was great strategy, and he never let up for the entire match. I liked the slow heel turn that was building even through the match, as he became more methodical and ruthless, just taking Austin apart. And Austin sold the leg for the whole damn match. Even on offense, he was always selling.
The finish was fantastic. Austin milked the submission for just long enough before passing out, and he really made himself look strong and admirable in defeat. Likewise Bret took things up a notch after the match and his facials and body language made him seem like a sour, mean bastard. It was just great stuff. Basically a perfect match.
In comparison, the Royal Rumble match was very good but not special in the same way. It's not going to be remembered in the same way, it didn't have the same impact on the company and it just wasn't as good a match.
It relied too much on the big spots. They were thrilling to watch, and Lesnar did look like a beast by kicking out of so much, but I think they could have accomplished the same thing without making the finishers mean so little. I also thought that some of the interference was unwarranted. J&J were involved in a couple of cool spots, but I thought they probably added less to the match than they subtracted from it.
Then there was John Cena. He just subtracts from most of the matches he's in.

Cena can have good matches for sure, but I don't think I'll ever consider a match with him in it a 5 star classic because there's so much he doesn't do well. He can tell a good story, and he works well with the crowd. He has a good sense of timing. But his moves
all look bollocks. Without exception. He also sells terribly. He jumps up when he takes the curb stomp, it looks ludicrous. He also can't stay down for a believable near fall. As soon as the ref slaps 2, he does a massive kickout without fail.
This match also had the problem I have with all triple threat matches in that it was just a series of one on one matches in the ring. WWE always rely on this technique particularly. Compare this to Joe/Daniels/Styles which is coming up later in the tournament, and you'll see a big difference. Those guys actually try to do spots that incorporate three people. I would have liked to see the two triple threat matches paired against each other actually.
There was a lot to love about Rollins/Lesnar/Cena without a doubt, don't get me wrong. I liked the match a lot, it's still probably been the WWE match of the year. Lesnar and Rollins tore it up out there with some great spots and outstanding selling. But it doesn't compare to the near perfection that was Austin/Hart. This is an easy choice for me.