I prefer a single stage for 3Gun also.
If he'll settle for single-ish stage I'd send him here to order a Geissele Super3Gun or the Dynamic (flat) version. I've tried two flat triggers and just can't get used to them.
http://www.primaryarms.com/ar-15-triggers/c/101100/filter/100000001298eq100000001371/CMC single stage triggers are also popular and are good, but at that discount price I'd get the Geissele all day.
I know some people that rave about the AR Gold trigger. I've never used one, but I've noticed that the people I know who rave about them are pretty band-wagon-ee sort of people.