I prefer the MP-5 rifle submachinegun. used it for 6 years while in the service
it was far more reliable, easier to maintain, more durable, and just simply far easier to use in combat than any of the m16 line of weapons.

http://www.hk94.com/hecklerkoch-mp5.html
( the second picture of the police officer holding the MP-5 with solid stock is the same varient I used)

it was also very useful in that the MP-5 rifle and my 9MM barettas ammo was interchangable

most SF teams leave the m-16/M4 in the armory and only use them in yearly qualifications or for parades