I am only familiar with the SAT. Where do you plan on going to college? It would be helpful, I think, to see what test scores those schools require. Here in the US the SAT is the one most schools look for. Students take the PSAT during their junior year and the "real" SAT sometime during their senior year, early enough to get the results sent to the schools they are interested in. It can be taken more than once here, so probably an earlier time for the first attempt is good. Then, if you don't score as high as you'd like, then you can re-take it.

As I say, though, this information holds for the United States.....