Alyssa Elizabeth, I am a current high school senior who took both the SAT and ACT
Personally, I would look at sample tests (or at least sample questions) of both (normally you can find these online) and see what's best for you. I actually tend to do better when I don't do any intense studying, but you may be different. I took the SAT twice and didn't get the scores I really wanted, but took the ACT once and got way above what I wanted, without studying. It really depends on what you're better at. If you're better at math and science, and prefer more straightforward questions, I would take the ACT. But if English and Writing are your forte, the SAT might be better for you. If you plan on taking the redesigned SAT, Khan Academy is great for that (and free). You can study for the current SAT and the current ACT the same way, just review science and math for the ACT. Honestly though, take a look and see what test suits you more, so you don't waste your time taking a test that you don't think you'll do well on. I learned that the hard way.