Both are the same if you see the name (almost). In term of performance they are totally different m4a4 has a wider spray pattern and little different to control on the other hand the m4a1-s has a smaller spray pattern and spray pattern is quite easy to master . In term of damage m4a4 does less damage then m4a1-s not that much of a difference when target is close.When target is on the other end or far away form the enemy the story changes m4a1-s does a lot of damage then its counterpart . One huge difference the m4a4 is more accurate if you are running and shooting at same time then m4a1 (don't known why).Just like everything something has pro and cons