Wow, I know too much about this.
In Connecticut, Manchester is considered the most successful, followed closely by Norwalk. Norwalk has way more financial resources, meaning they give more scholarship assistance to students and can provide more extensive programming in some cases, but Manchester's reputation for national recognition is untouched. (Quick example: It's the ONLY college in the country to have ever successfully nominated a Truman Scholar...and they've done it FIVE TIMES. Five Jack Kent Cooke Scholars, too, plus a slew of All-USA First Team members, Guistwhite Scholars, etc.) It also attracts more national faculty and administrators, though Norwalk is starting to catch up with that. Manchester is considered the flagship of the Connecticut system - check any news articles about the system, or the fact that for years, they were the only one to have articulation with UConn's liberal arts college - so sorry, Norwalk students, even though I love you and your school.
In New Hampshire, NHTI in Concord, definitely. I think the fact that they have a large residential population helps. In Massachusetts, you could make good arguments for several of them, but I would lean towards Quinsigamond in Worcester or MassBay in Wellesley - like with Manchester, you simply can't argue against their scholarship and transfer successes. Bunker Hill has a lot of success simply because of its sheer size, but they cater largely to ESL and developmental students.
A lot of the NYC community colleges are genuinely outstanding. Same for a lot of the Illinois ones, especially DuPage and Elgin. And Texas is really good to its system, especially with schools like Cy-Fair that serve as national models in a lot of ways. Valencia Community College in Florida is known for having the best honors program of any community college in the country, and Miami-Dade has a reputation for putting out really successful graduates. For California, Santa Monica and De Anza are givens, but don't forget colleges like Butte College that have amazing honors programs as well.
And yes, Mercer is really good, but oddly, so is Essex County College. You wouldn't think of a Newark college as attracting fantastic students, but they do. The New Jersey system as a whole is pretty exceptional.
Okay, enough from me.

But this is my research area, so...you got me going.
Edit: Wait, forgot one thing. For people linking the so-called "rankings" for community colleges...those have been roundly trashed and discarded by researchers and advocacy groups, including the AACC and AAC&U. That survey was incredibly flawed and included a lot of colleges known for being UNsuccessful in a lot of ways, not shining stars. Just something to keep in mind.