I am guessing you are a junior?
It would be good if we had more context. Are you aiming for a top college? I suspect that many top colleges will ask for test scores next year, but it’s hard to know right now. If you are a junior and are aiming high, you have plenty of time between now and then to decide if you want to do the SAT or ACT.
I see no reason why you must plan on taking both tests multiple times. Try a sample test of both and go with the one you prefer. If you need to retake, or want to try the other test, you can decide later. They are similar enough that you don’t have to spend a lot of time trying to prep for the other test.