As true dark horses that have at least a small chance of winning a title, I will go with:
1A - LeRoy (Everyone seems to have Althoff and Lena-Winslow ahead of them, so this should qualify.)
2A - Chicago Christian (They have a difficult path and no playoff pedigree, but their only loss was to 4A Wheaton Academy.)
3A - St. Joseph - Ogden (Although unbeaten, clearly both Byron and Montini would be considerable favorites over them.)
4A - Normal University High School (They are battle tested in the Central State Eight.)
5A - Morgan Park (Forget the Chicago Catholic League, let's go Public League here.)
6A - Geneva (I will stay away from the Flyers as long as possible and go with a DuKane co-champ.)
7A - Downers Grove North (The Trojans regain early-season form and sweep to the title.)
8A - West Aurora (Do you believe in miracles?)
Edit: After posting the picks above, I checked the CalPreps rankings to make sure the teams could reasonably be viewed as dark horses. I believe they all can be viewed that way. Here are the CalPreps rankings within their respective classes:
LeRoy - 3rd
Chicago Christian - 6th
St. Joseph - Ogden - 4th
Normal U-High - 11th
Morgan Park - 7th
Geneva - 3rd
Downers Grove N. - 7th
West Aurora - 18th
All are ranked 3rd or worse, and even where they are as high as 3rd or 4th, they are ranked behind powerhouses such as: Althoff and Lena, Byron and Montini, East St. Louis and Cary-Grove.