Definititely take the ACT...I personally did FAR better on it compared to the SAT.
Tips:
1) BE SURE to bring a snack and water to consume during breaks.
2) Bring a watch, because the proxy place isn't required to provide a clock.
3) Don't freak out during the Science section. ALL of the information you need to know to answer the questions can be found in the text provided.
4) In the Reading sections, the answers require a lot less interpreting compared to the SAT. If you find a quesiton that you can't immediailly answer, chances are it can be found directly in the text.