Ok what's the differences? Auto, semi, different coatings? one better with different barrel/gas lengths? Looking at a 16" 223 wylde with a mid length gas system, but thinking I might want to bump up to 18" for noise.
Don

In my experience, the standard "full auto" BCG that has been Magnetic Particle Inspected (MPI), has the key staked, and is parkerized works just fine, no matter the gas system length.

You don't need Nickel Boron or Titanium Nitride coatings unless you plan on swimming with it.

A longer barrel just puts the muzzle further away.

You can get a linear compensator that expels the gases and noise forward, or get a suppressor.

GEorge

Depends on your uses.

A lighter BCG will cycle flatter/quicker with an AR set up for competition with adjustable gas-blocks, light buffer, light ammo, etc.. Basically giving up some reliability for performance.

But for a defensive AR shooting normal ammo and non-adjustable gas block, go with the auto bolt carrier. The extra weight delays bolt unlocking a little bit = better for bolt lugs and extraction, easier on the system overall. More forward momentum to strip rounds from the mag too in dirty conditions.

The muzzle will seem to jump less, especially when combined with a heavier buffer.

I took 2 colt 6920's to the range one day:

One with the stock H buffer
One with an A5 buffer "0"
An extra A5 "3" heavy buffer

The muzzle jumped least with the A5 "3" buffer installed and rapid fire at 25 yards was definitely easier/faster.

Just make sure the bolt consistently locks back on empty with the weakest ammo you will likely use.