What is better: M4A1-S or M4A4 in CS:GO?

First, I have to say that M4A4 technically better in the current patch (11.06.2015.) but let's look at everything step by step :)

M4A4 advantages:

1. Damage. M4A4 is little stronger than its alternative in this terms.
2. Spray. In the current patch, M4A1-S has more complicated spray and the weapon has become more difficult to control at close to medium range.
3. Amount of rounds. M4A4 has larger clip.
4. Tactics. With M4A4 easier to hide because of the size of the weapon and you can cs go backache without fear of run out of ammunition.

M4A1-S advantages:

1. Accuracy. M4A1-S more precisely, it is much easier to aim at long distances by short bursts.
2. Silencer. If you quick kill enemy in the back or side before he noticed you your late position will remain unknown.

Professionals: Players on tournaments usually play with the M4A4 now. Rifle with a silencer generally used by snipers who did not re-learn in the new patch. Until this patch all mainly played with M4A1-S. So, when the two guns were balanced professionals prefered rifle with the silencer :)