I hit the ceiling on one test and nearly so on the other and took both over 20 years ago. I understand the SAT has changed significantly since.
IIRC, the ACT was a lot more fun and more fact based when it came to the math and science sections. I felt I could grunt out the answer based on what I knew. On the SAT I had to think hard about some questions. On both tests, being able to quickly finish easy problems and checking your work was essential.
On the verbal side, the ACT was more about the mechanics of grammar and comprehension whereas the SAT was about shades of meaning and knowing obscure vocabulary words.
