I am going to get an air tank for my truck and debating sizes. I am going to run Arb's front and rear, air lines for 37 inch tire filling and potential air tools front and rear.
The truck is a f350 cclb so I have tons of space.

Do I go 9 gal? 12 gal? As big as I can stuff in the spot I am going to fit it in?

Any reason bigger is not better on this one?