Flash Suppressor reduces the bright flash that happens when unburned powder leaves the barrel and hits the air, instantly catching fire. Minimizes the fireball to avoid giving away your position or messing up your night vision.
Compensator vents the combustion gas upwards to counteract, or compensate, for muzzle rise. Really helps you keep the muzzle down during rapid or full-auto fire - but some comps actually increase muzzle flash.
Muzzle Brake reduces felt recoil by venting the gases, usually through the sides of the brake, so they actually push the gun forward. Makes the gun a lot louder, and side-vented gas isn’t very fun for other shooters or observers positioned off to the side.
Quick Tip : How to Change a muzzle device on a AR-15
Tech Tip : Suppressor Introduction