The M4 is my personal favorite. While they shoot a rather lackluster round (.223/5.56), they more than make up for in accuracy. A lot of different brands flood the marketplace these days, but if it goes bang and shoots straight, it doesn't really matter. I prefer mine to have a foregrip and a red dot sight (I have a Sightmark attached to mine). With an effective range of about 600 yards (you have to really know what you're doing at this range, however), you can reach out and touch someone at a very long distance. With proper maintenance and care, it's a weapon platform designed to never fail under duress. The maintenance for the rifle is dead easy, you have to be really thick to not understand at least the basic cleaning procedures of it. It's light enough to be utilized on long-range patrols and for small enough to be used in close quarters combat. In a pinch, it can be used as a short-range sniper rifle.