Having fired the civilian versions of Smith & Wesson MP15 AR, Tavor and SCAR-H during a recent trip to Michigan, I personally prefer the Tavor or SCAR, Tavor's ease of use makes it a no brainer, point and shoot, the M4 is slightly more accurate while SCAR is the badesst weapon I have ever fired. Loved the quality of all the weapons. I can see why professional SF units choose on of the 3. Love the balance of the Tavor, trigger action of the SCAR, however with the AR I was the most consistent with around 25 headshots from a 30 round mag while at a range of arond 50-75 meters. SCAR-H packs a punch, I can assume in full auto it needs a person to be trained a bit, the recoil though manageble tends to have an impact on the shoulders, but hey I was firing in my T-shirt with no padding seen on most modern plate carriers. During this time I also fired the FNX .45 pistol, what an amazing pistol.
The AR and Tavor are ideal for double tap use, the recoil is quite low and one can easily lay down 2 shots with in an inch. SCAR-H is a one shot kill weapon, hit anywhere above the waistline and one goes down, however in a double tap, I could manage around 5inches of round separation. I guess the pros can get it down to with-in a couple of inches.
The SCAR is also louder, it's a scare the piss out of your pants weapon and I was nervous when I held it the first time. Next time I'll try to fire the SCAR-L.