Didn't see your post when I was posting mine, but anyway -- CP210x.
I use FTDI because I can easily run comm ports at 3 Mbit/s. OSX (and I think Linux too) does support comm ports at non common baud rates. I'm looking for a way to add decently quick USB comms to a device without writing my own drivers. FTDI seems like the only option. Using HID is limited to 64KB/s.