I think many forget how and why a muzzle brake
works. It is simply a device to divert exiting gases from going straight ahead. It does not affect rifle accuracy at all (proper install required of course).
The bullet is in front of the gas front so acts as a stopper/cork. This helps force the gases to travel sideways. This is why you want the brake bore to be as close to bullet diameter as possible. However, it must still be large enough so that the bullet does not hit the brake during its travel. 0.020" over bullet diameter seems to be a good compromise. The longer the brake, the larger the bore the ports furthest from the muzzle should be.
How it does affect accuracy is that it changes the barrel harmonics. Some will test using a muzzle brake then take it off for hunting. Bad idea unless additional testing is done to confirm the load in the 'new' barrel and POI.
Have yet to find a rifle that would tolerate removing a muzzle brake without some adjustments.
Like Kirby, I prefer the partition or fish gill type brake. Bigger is better at reducing recoil. The multiport singe expansion chamber brakes are not as effective. Anytime you allow gases to travel forward, you reduce its affectiveness. The more effective a brake is, the louder it will be perceived. Simple a relation to amount of gas diverted and direction of diverted muzzle blast.
As they say, no free lunch. Unfortunately, we are not blessed with being able to shoot silencers. If we were, we would have the best of both worlds - recoil reduction with quiet shooting.
I have had very good luck with a Micaluk (sp?) AR15 brake. Very similar to the Holland in style and equally effective..
As to indexing, it has no effect on accuracy. It simply causes the rifle to not recoil straight. But that can have it uses too...