It depends, below is a comparison of both weapons.
Pros: 1.Lighter, and more compact.
2.Customizable to a higher degree
3.Specificaly designed for CQC
4.Telescoping butt-stock can be adjusted to fit ones liking, and can extend out to 5-6 inches
5.Has fully-automatic mode of fire, along with 3 round burst, and single-shot
6.Can be used in virtually any situation
Cons: 1.It is only well suited for Low to Mid ranged firefights
2.Because of shorter barrel the Muzzle velocity is significantly lowered
3.Range, along with power, is significantly lowered due to lowered Muzzle velocity
4.Ammo can be depleted easier due to fully-automatic mode of fire
Pros: 1.Is incredibly accurate at long range
2.The 3-round burst mode in place of a fully-automaticmode can slow down ammo depletion
3.Long barrel grants high muzzle velocity, thus granting the M16 superior range, and power
4.Also has a Single-shot mode
Cons: 1.Is not very Versatile due to lower degree of customization
2.Only has 2 modes of fire (3 round burst, and single shot)
3.Although the 3 round burst can conserve ammo, it isnt as effective as Fully-automatic fire in close range ancounters.
4.Lightweight, but still Large in terms of length