The M4A1 is the most heavily supported modular platform in Arena Breakout: Infinite, which is exactly why choosing a configuration is difficult: almost every slot has three defensible answers.
What actually matters
Vertical recoil is the stat that decides whether you win a sustained exchange, and it responds most strongly to the muzzle and stock slots. Everything else is secondary.
Budget tier
Under 80,000 Koen configured. A competition brake and a CTR stock give you most of the available vertical recoil reduction for a fraction of the cost of a suppressor. Run green tip.
Balanced tier
Around 135,000 Koen. This is where a suppressor starts to earn its slot — not for the recoil, but because it removes the muzzle flash that gives away your position in every interior fight.
Meta tier
Above 250,000 Koen. The sixty-round drum is the single most expensive attachment on the platform and the only one that changes how the gun is used rather than how it shoots.