Which is harder – the SAT or the ACT?

Neither one is harder – certain students are simply better at one exam or the other. The ACT is more straightforward, but also more objectively difficult. The SAT has easier material, but it asks the material in trickier ways that involve more logical reasoning. The only way to figure out which one you should take is to take diagnostic exams for both tests, compare your results, and then stick with the one that gives you the best score.