Either are fine. I recommend taking both tests.
Past CGA test scores:
SAT M-V median scores are in the mid 600s
ACT composite median scores are in the high 20s-low 30s
in the AFA academics in general are 60%. Its probably somewhere close to that but I don’t have any exact number for you.
Hope that at least helps a little!
Your standardized tests are important, but just one piece of the whole person index that any SA looks at.
This year is forecast to be as, if not more competitive than last year's cycle for SA candidates.
I suggest, if financially possible, to take both the SAT and ACT exams, keep your class schedule filled (no early, late dismissals) with Honors, AP or IB courses that stress math and science, keep in shape with running, sit-ups and push-ups (couldn't stress this enough!), continue to volunteer, play your sports, keep active in school and most of all keep your record clean.