First off welcome, MuNgEr
with respect to to your barrel choice, it would depend on the type of shooting you plan for your rifle.
Most members here - based on 1,000's who have offered opinions - say the shorter barrel of any two options is best. You will not sacrifice accuracy, reliability, or performance of any kind with the shorter, but you will save weight, and have a rifle that is fractionally more maneuverable.
In fact, the 16" is the overwhelming favorite among new rifles, but if you are looking for a true Varmiter, you may appreciate the added reach of the longer tube.
Best advice?
Spend a few days here reading the various forums on what guys are using and look at what they experienced.
It could end up saving you hundreds and almost surely will help clarify your options
Good luck and keep us posted on your rifle.