Is to take a FREE diagnostic test of both the SAT and the ACT, and then compare your scores. That way, you can see if there is a clear winner and one test starts you off with a relatively higher baseline to work off of, or if there isn't, you can flip a coin, and choose which one to study for. 

Colleges view the SAT and the ACT completely and utterly the same. There really is no test bias, and so the best thing you can do before spending your time studying for the test that that is not best for you, is to determine which test is worthy of your time in preparation and $$ if you are signing up for a course.