I've been to a few different clubs in the city, and I've always liked NYSC best because it was one of the most unpretentious - it's not a place where one goes to "be seen", it's not a spa, it's a gym. People sweat. They wear shorts and t-shirts instead of spandex. I've met some great friends in some of their classes.
The club on 86th street consistently upgrades its machines, and supplies a lot of equipment, more than most gyms I've been to. They're renovating the whole gym now, so it's a bit difficult to navigate, but looks like they'll be done at the end of the month, and so far, the changes are great - lots more space, more machines, great stuff.
They also offer corporate rates, if you're able to benefit, definitely worth checking out.