I carry and AR-15 at work. We uses Colt and they are excellent. I would say Colt and Bushmaster are probably the top brands. We have little 4 power ACOG scopes on them (combat scope) The ones I have handled seem to be very reliable. We qualify out to 200 yds., father out than that I don't have any experience and as far as grouping goes they seem to shoot pretty tight groups although we typically don't train for marksmanship as we are more into combat shooting.