Having a few boys in the CC system makes me eminently qualified to answer this:
WITS often gets the most serious guys. R’ Zachai, the 1st year BM Rebbe is considerd by some to be the best in the system;
MIAMI also gets serious guys, but they have a drop more fun then at WITS. Guys are very attached to the Rebbeim from there;
ISRAEL – as noted, a mixed bag of types, but all are very “good boys”, regardless of their learning skills. Not all are from CC high schools.
With the other branches, I’m not as sure. VALLEY TORAH sometimes gets weaker guys. But that can vary (as is true of all branches) from year to year.
Some guys, when they come back to The Hills for 4th year, are doing things like TTI, Fairleigh Dickenson, and other “alternative” programs. But it’s not officially “encouraged”.