It used to be the Cards. Two things have changed for me, however....
First, when CC went to to Chicago, I saw that as a betrayal. Yes, its a business...and yes, he got paid a boat load of money. But he could have gone anywhere else and the whole Brewer fan base would have wished him well and even rooted for him. He chose to go to our biggest/closest rival. He showed a complete disregard for the support and even affection he'd received over the years. That might sound a little soppy, but those fans are what keeps clubs going during the bad times. I really dislike that the local boy valued us not at all. So...while I used to enjoy the rivalry and thought it was kind of fun, now I root against the Cubs every day. (the whole "Wrigley North" thing also factors in ;) )
Second, we recently went to St. Louis for the series back in May. Fabulous experience. Really. Great people, good stadium tour, and we really enjoyed the baseball museum. The Arch is less than a 10 min walk from the stadium. The Amtrak/ Metro station is right there too. Baseball Village is really cool. So...while I'm NOT over '82, I do have an appreciation for their fans and the entire "baseball experience" in St. Louis.