I always liked the iron sights on the AR-15. I had a Colt scope on my first AR-15, but there was a tiny bit of play between the upper and lower. Not noticeable except it seemed less accurate with the scope than without it.
Someone made a wedge to keep them tight. I never tried it and it seems that today that is not a problem. Still I think I would prefer the iron sights, that is if I had one now.
NOthing wrong with iron. Worked for marksmen ever since firearms were invented. In many cases, I find that I shoot better with iron sights . . . although the newer electronic wonders appear to be much quicker on target . . . just put the dot on target and pull the trigger.
I may get blasted for this but spending big a large amount of money for a sight for an AR 15 is a waste. I own one and it has a very basic scope. I make very decent hits with it.