Welp, since everyone is doin' it and I am only a bout a year ahead of you ... here's my (basketball-specific) hot take!
TIER ONE: Undisputed Rivals
Indiana ... You're going to have fans who hate Iowa the most, some who hate Michigan the most, some who even hate Northwestern the most, but I think IU is the one program that will show up at least in the top 3 of 90%+ of Illini fans' rivals list.
TIER TWO: Somebody's Biggest Rival/Teams That Hate Us the Most
Iowa ... Bruce Pearl needs no explanation, and fans from the Quad Cities or Western IL are naturally going to despise the Hawkeyes. Plus, let me tell you, Iowa fans have an almost unbelievable hatred for Illinois.
Michigan ... That '89 loss is just so damn important and unfortunate, that they get here because of that. Some fans (rightfully) will never forgive them for that, plus they're Michigan...
Northwestern ... Most Illini fans don't get too riled up about NU, but we are probably their biggest rival, and they've had enough success against us recently to move into this territory.
Wisconsin ... Used to be bigger, but there are still a lot of Northern IL fans who have to deal with Badgers fans and hate UW. This Rivalry really should be a lot bigger, given Packers/Bears overtones.
TIER THREE: Some History, On-And-Off Rivalries or Basic Animosity
Michigan State ... We always had an oddly friendly rivalry with them before Izzo couldn't keep his mouth shut, but that died down quickly. Some might not like MSU, but they don't really inspire much hate. We've also been uncharacteristically successful against them during our down years.
Ohio State ... This got a little more tense after Evan Turner, but again ... this one has never been that intense in basketball, IMO.
Penn State ... PSU would be in Tier Four, but ever since they broke our home winning streak in 2006, they have been a VERY sharp thorn in our side.
Purdue ... I know, I know, some might consider PU a rival; after all, they are the closest school to Champaign, and we have had a lot of battles with them over the year. However, the mutual hatred of IU plus Purdue just giving off an, err, non-combative vibe even when they're good really dulls this one for me.
TIER FOUR: Never Had Much Animosity For a Long-Time Conference Foe
Minnesota ... Just not a lot goin' on there for a traditional Big Ten series. We're killing them in the all-time series, have dominated them since 2000 and we both have plenty of other rivals.
TIER FIVE: Who Cares?
Maryland ... No knock against Maryland, but they're so new to the conference.
Nebraska ... I find it so entertaining hearing Iowa fans talk about how much they hate Nebraska ... Nebraska?? How? Lol.
Rutgers ... Again, just too new.