it's better to take both and send in the better score.
Very true...emphasis on better score. However, be cautious. When registering for the ACT and SAT, there's an option to have the scores sent gratis to a limited number of colleges and your high school. I suggest to not avail
yourself of the option, especially the high school. Once they have the scores, the GC will most likely include them on your school report/transcript that is sent to your colleges. By supplying them to the high school yourself, they can only report the scores you give them and want reported.
Vassar, as well as Hamilton, Middlebury, et al, will inform the prospective students to send all the scores and allow the college to decide which scores to use--presumably the best. The problem with that approach is once the admissions officers have seem the scores, and assuming the SAT subject tests and/or the SAT are not as impressive as the ACT, or vise versa, the admissions officers have seen the lower, less impressive scores. Admission officers erasing the less than favorable scores from their minds eye isn't possible. Any more that when a jury hears testimony that a judge subsequently directs them to ignore. Won't happen.
Once you have the results of both tests, you can decide which scores to send. It will cost a fee to send the scores to each college, but I believe it's a small price to pay to control the process and dictate which scores are considered for admission.
Lastly, one advantage of taking/submitting the ACT/writing in lieu of the SAT is that the two required SAT subject tests are waived. Many students do not do as well as expected on the SAT subject tests. Of course, many score higher than expected. Have you considered Wesleyan U ? They have a very good film program, and the college has a similar student profile as Vassar. USC also has a great film program.