I have a relatively short attention span and have trouble sitting down in one spot for long hours. Therefore, which test do you think would be less tiring? Thanks!
You may want to consider applying to a few test optional schools.
Take a timed practice test of each; see which comes out better and focus your attention/prep on that test. Do you have a 504 plan at school?
Both tests are over 3 hours long; however, as one commentator already referenced, if you have a 504, you may be able to get a special testing arrangement.
The ACT is a more straightforward but faster paced test while the SAT has longer questions and requires more thought into each question, so the ACT may feel more comfortable for you.