Well, I see we're getting to the more difficult questions now.
To me at least, this question seems somewhat silly.
All idols I cheer for have a special place in my heart.
After all, who would waste that much time, money, and energy for someone they don't feel for?
Closer to heart would be family members, close friends - and so far I don't think any idols have got that close.
So following my all idols answer, have a pic of Mobekimasu, just cause I can't be arsed to look for photos of other groups I care about: