2" would be a complete waste if you ask me. Airflow goes down drastically as you lower pipe size. Do at least 2.5"
Both your options would add weight to the suspension itself but if its aluminum it would be minimal. I think getting under the car and looking at how much room you have for various options is your next step. Drive it up on ramps so you see how everything looks at ride height. Both would work decent but not as much total airflow as from the front. Personally if I were to do one I'd do the scoop mounted on the arm, the other method is tougher to get the air going exactly where you want..