Play Meter covered the show in its 1/15/81 issue, which actually had three separate articles, reviewing the show.
First was an article by Dick Pearson titled "Play Meter plays the games"
Unfortunately, Pearson didn't name a standout game, noting "But since Space Invaders, we have seen something new added to the games, which makes it all the more difficult to pick a 'Game of the Show." He then goes on to further discuss how difficult picking standout games is and doesn't name a game of the show.
Nonetheless, he does discuss the following games as among the standouts: Battlezone, Berzerk, Star Castle, Defender, Spectar, and Space Tactics, and also mentions Radar Scope, Zero Hours, Uni War S, Space Panic, and Crazy Climber.
Here's his take on Pac-Man and Rally-X
Hmm. He doesn't seem to favor one over the other. Plus he also mentioned a lot of games, so this article may not be of much help.
Later in the same issue we have Dick Welu's show diary. Welu is much more forthcoming with what games he liked and disliked.
He calls Star Castle a "honey", was lukewarm on Space Panic, and liked Battlezone.
His pick for game of the show?
OTOH, he did pick a Bally/Midway game as "sleeper" of the show. Which one?
Yep, he picked Space Zap (!!???) as sleeper of the show. Now don't get me wrong, I loved me some Space Zap back in the day, but sleeper? Really?
Finally, we have the article "An Independent Review: Standout games at Chicago Show" by Tony Licata. Ahh. This is just what we're looking for. He actually picks four standout games of the show.
And they are....
wait for it
That's what he picked. Pacific Novelty's Deep Death (which was subsequently renamed Shark Attack).
OK, so it looks like Play Meter didn't consider Rally-X the standout game of the show, or even significantly better than Pac-Man.
What about RePlay?
Here's a review of the show from the 12/80 issue
What about the other claim, that Midway initially liked Rally-X more than Pac-Man? That claim actually does hold water. Midway president Dave Marofske said as much to Kent. When I talked to him circa 1999, he told me pretty much the same thing:
Far more interesting was a story that Game Plan exec Ken Anderson told me. First, a little background. In the end, Namco chose to license the four games to two different companies. Midway got Rally-X and Pac-Man, while Game Plan got Tank Battalion and King & Balloon. Ken Anderson was an executive at Game Plan at the time and over the years it seems he worked for half the manufacturers in the industry. How did Midway end up with Pac-Man? Here's what Anderson told me
Bonus. Another famous myth.
Earlier, I mentioned Donkey Kong myths. One of the most famous is that it was originally called Monkey Kong and the name was only changed to Donkey Kong due to a translation error (in some versions, due to either a blurred fax or a misheard phone call depending on who's telling the story).
That story is considered "busted". There's even a longish article on it at Snopes.
Recently, however, I came across the following from the October 1, 1981 Play Meter
What? Monkey Kong? So is the "busted" myth not a myth after all? Have I found holy grail of video game mythbuster-busting? Alas, I think not. I'm pretty sure this is just a good old fashioned typo. RePlay referred to the game as Donkey Kong the month before this issue came out and may have done so earlier. But it did give me a brief rush of adrenaline.