A chrome-lined barrel cleans faster and lasts a lot longer; there's a reason the gubmint uses 'em. Colt and Bushmaster have the best barrels and of the two, in terms of bang for the buck, I'd pick Bushmaster. I agree that a flat top receiver is nice for optics but the detacheable carry handle with A2 sights are more durable than any back up iron sight (in addition to being less expensive and looking more "correct"). Make sure to master the iron sights before going to optics, and IMO if you're only shooting at 100yds don't even bother with optics.
"Laws that forbid the carrying of arms...disarm only those who are neither inclined nor determined to commit crimes...serve rather to encourage than to prevent homicides..From "Commonplace Book" by Thomas Jefferson.