Okay, I'll try to give you a place to start. First, what is more important, having a rugged, reliable field weapon, or having a tack-driver that is more prone to jams and needs more maintainance?
If you want the rugged, reliable field weapon, you want two things:
1) A chrome lined barrel and chamber
2) A relatively loose chamber
The chrome lining will help protect the gun from corrosion, especially if the gun is ever taken into the field. The loose chamber will help if there is any dirt/fouling in the bore, and will help overall in dependability (especially with slightly out-of-spec ammo). Both Colt and Bushmaster have both of these on their non-competition guns.
If you want a tack-driving competition gun (or just want to occationally take it to the range/varmint shoot) then you want a non-chrome bore/lining and a tight chamber. Both of these will TEND to help with accuracy, and all of the really good match grade barrels are like this. All of Armalite's ARs used to be like this, but I hear they are changing over now. Olympic Arms has made their name with tight chamber/non-chrome guns.
So there it is. By the way, the rugged, dependable loose chamber/chrome-lined guns still shoot very well, so don't count them out when it comes to accuracy! These stock field weapons guns should come close to (or achieve) MOA with the right ammo. Whatever you decide, do it quick. The price of ARs is steadily climbing, and will prob continue to do so through the end of the year. And I apologize for adding to the Y2K buy-every-gun-paranoia!
HTH!