Very era dependent for JCA.Who is Your Teams Biggest Rival?
What is your most memorable game between them?
Has your rival team changed throughout the decades?
It was undoubtedly MC through much of the 90s and early 00s. Prior to that it was the Illini 8 and some local public schools., but they all were up and down in their levels of success. Marian Catholic was one of the bigger regular season games for a good stretch too.
Morris was the playoff nemesis of the 90s and 2000s, but the last decade or so has been lopsided the few times they have met.
For a short period in the 2000s when the ESCC was a closed conference and Carmel Mundelein was near their peak, that was the biggest regular season rival.
Naz and Montini have been playoff thorns over the last 10-15 years, but it's hard to classify that as a true rivalry. They are essentially serving the role Morris played 15 plus years ago now, though the results are not always as favorable.
Really the best answer for JCA over the past 20-25 years is Providence. Starting with matchups in the mid 90s and mid 2000s, both teams would always be highly ranked and there were times each was the overall best team in the state. Games were tense and emotions high when they matched up. That is the game the kids, team, and schools seem to get most hyped up for.