6.8 Build Questions

I am going to get a barrel/bolt to convert my current 5.56 to 6.8 so I can hunt with it. My question comes down to barrel length 16" or 18". What would be the main selling point in going with 16" vs 18" and vice versa. I currently have a Daniel Defense 14.5" CHF barrel.
Rest of the gun:
Mega Arms Upper and Lower
Geiselle 2 stage trigger
12" ALG Defense handguard
I'm also going to change out the buttstock to an adjustable one just not sure which one yet.
I will get into reloading but for...

6.8 Build Questions