Heres a good article:
What's the Diff?: Grassroots Motorsports Magazine Articles
I've used Nismo, KAAZ, Tomei, and OS Giken, and OS Giken is hands down the best LSD out there!! It never needs a rebuild, has true 100% locking capability, zero chatter, and linear lock up. They even told me that I only have to change fluids after every 20,000 miles!! Compared to KAAZ or Cusco recommended 5000 mile oil changes, the OS Giken is a better investment.