from my knowledge:
Of all the JCs I think CJC has the best history of producing good musicians. The Sexies, Her Liquor. These guys tend to be the most "qualified", alot of classically trained pianists and vocalists, church musicians, and can do good stuff with harmony. Their annual Rockafella gig is well organized and handled with good sound and good bands.
RJC has a pretty decent music culture, they have a Rock CCA and a Jazz CCA, and they're home to bands like Triad. It's quite all rounded.
Schools like TJC, VJC and TPJC all have their musicians and they also have alot of supporters. There are some stellar quality musicians here and there and there are also alot of people who just start picking up instruments, but the culture and support is good stuff.
Not too sure about other JCs. I remember NYJC was having some sort of Idol-esque competition when I was there for PAE, but I think almost every JC does this nowadays?
I think IJC has some serious metalheads in there. Some of the VS metalheads went on to VJC and MJC too.
Just my rough idea, I might be wrong!