Recommendations on Multi-channel USB 2.0 Video (NTSC) Fram..

I am looking at 4-channel USB2.0 Video (NTSC) Frame grabber devices and
there seems to
be slew of them out there, all bundled with different kinds of
monitoring and
DVR software. I intend to access the video from my own code
(preferably
a modification of my usb webcam application). I gather most of the
devices
are based on a few imaging chips (i.e. Phillips SAA7113H). What are
some
of the alternatives (chipset) and which one has the most decent
throughput (min 10fps, 4 channels, and a reasonable image quality)?

Thanks,
Ben