Depends on your familiarity with the mission/raid/strike, or if you're doing pvp or pve. PVE I'd MUCH rather have a stability perk than third eye. Id almost rather have anything than third eye for PVE guns.
English
-
I have yet to get a gun with third eye, so I can't agree or disagree :P However the field scout is the more important perk of the two IMO considering 22 rounds goes by very fast lol.