Last year I purchased a Bushmaster 16" A3. I love the gun to death. I have the 16" barrel without a compensator or flash supressor. The rifle is VERY loud and has a massive flash signature. (on the range they call my rifle a flame thrower) I have considered the AK or Ycomp muzzle breaks, but don't know if they will make a difference? Will adding a muzzle break affect accuracy at all?  

A Smith compensator won't hurt accuracy at all. Won't help with muzzle flash or noise, either, though. It does keep the muzzle level during rapid-fire, too.

I have an AK brake on my Bushmaster M4 14.5" upper. I was very impressed with the recoil reduction. The flash signature is small for a muzzle brake, it's roughly around 2" in diameter and 6" long and diffuse. Much less than a stock barrel without a flash suppressor. I had a chance to check it out the AK brake at dusk the last time I went to the range. It produces a fairly dim flash and is parallel with the bullet path. The AK muzzle flash won't obscure or flash blind your sight picture in the dark as much as other brakes.
I didn't notice a difference in accuracy, I was shooting much better that day with my M4 than with my 20" standard Heavy barrel. Although I was messing around with sighting in cheapie scope on the 20".

There is no accuracy loss. I have an AK brake on my shorty Bushmaster. I like it, and it protects the crown. I would recommend it, but I don't think you will lose a lot of flash, mine just seems to redirect it. looks awesome at dusk. [pyro]