Colombian guerrillas.
As a Columbia, SC, native it is my prerogative to ask “How 'bout them Cocks?”
That story alone made this thread worth starting. 
As a rabid Arkansas Razorbacks fan, the only appropriate ending to that sentence for me is hogs!
Astros.
My 6 year old nephew once sat down next to me and said “How 'bout those Vikings?” Of course he was talking about the guys who sailed the North Atlantic raping and pillaging.
Nevermind.
Adding to what JohnT said, of course we have people here (Tucson) who are big fans of the Phoenix-based pro teams. But not having any pro team here locally, it’s natural to root for something closer to home. (The “Toros” don’t count. They’re a low level successor to our recently departed Class AAA baseball team that relocated to Reno.) Especially since over 36,000 students attend the University of Arizona and Lute Olson, the retired basketball coach, is something of a living legend here. People here are much more likely to say, “Howza 'bout them Wildcats?” than D-Backs, Cardinals, Suns, or Coyotes.
Cubs.
Reason: I don’t keep up on sports, so I can’t really discuss how any particular team is doing… except for the Cubs. Not that I keep up on them, either, but you can count on the fact that they’ll do just well enough to give the true fans a bit of hope, then choke when they reach the playoffs. Every time. I have a friend who’s a die-hard Cubs fan, and this seems to be the way it always plays out.
In all of the 25 years I lived in NYC, it was always “How 'bout them Mets!” Even, I think, in their off-season.
No, no, no. 
I used to live in Chicago years ago. It’s definitely, “How 'bout them Cubbies?”
If this were Match Game, I would answer “Dawgs”.
I considered that too. I remember Roy Rogers saying it on the Flip Wilson show. But I went with Dawgs because it seems to be that “how do you like them apples” is the more common version of that phrase.
That phrase has more to do with being impressed by something than it does trying to change the subject. At least, in my experience.
Have you thought about running some counts on the input? I’m suspecting that Dawgs is way ahead but there are definitely some contenders. It’s your thread or I would do that counting.