The debate needs perameters. But if there are none, any selectible locker is better than the detroit. Whether it is ARB, OX, KAM, whatever. The "problems" that your buddy mentions about ARB reliablity are mentioned by people who want the ARB but don't want to pay for it.
I will tell you this to stir up a hornets nest. Nobody serious about rock wheeling/racing/really getting it, ever runs a detroit. They will weld up the diff before running one. I have two cars, both run a selectable and a spool, just on different ends.
2009 King of the Hammers
BUCK Wild Racing
Co-driver: Pat Quirk
Rover Tracks www.rovertracks.com
DJ Safety www.djsafety.com
West Coast Rovers www.westcoastrovers.com
Reel Driveline www.reeldriveline.com
Made it further than half of the other guys, but the Hammers won.