Best lightweight 20-22" barrel for accuracy and lifespan (durability) ?

[A5BLASTER]

Any of the barrels you listed should give you what you are looking for, As for as the jp scs and adjustable gas block. I run both on my 21 inch grendel and love them but I dont use a light weight bcg just a normal bcg.

I bought the scs that comes with the spring kit, add that with the syrac adjustable gas block and it is a very smooth running rifle

I use the syrac because the adjustment screw has a detent and not a locking screw and the adjustment screw is on the front of the block much easyer to get to adjust with a handgaurd on, very nice click adjustments as well.

Hope this helps