Question: Should I take the World History SAT II after I finish AP World History this year? I am only a sophomore, and I don't know many people who have taken SAT IIs at the end of their sophomore year. Additionally, I would like to know which SAT IIs the competitive colleges prefer to see. Are you limited to only three?
You should definitely take the World History SAT II this year. It's always a good idea to try the SAT II as soon as you've completed the corresponding course, assuming that you won't be taking a more advanced version of it later on (e.g., if you are taking chemistry now but will take advanced chem next year, you'd be wise to wait.) It's actually fairly common for sophomores to take SAT IIs, especially students pursuing challenging academic programs, as you are.
While competitive colleges don't have "favorite" SAT IIs (especially now that the Writing SAT II is being abolished due to the new writing section of the SAT I), they do like to see a diversity of tests. For instance, if you can score well in history, math, and science or in history, science, and foreign language, it will "look better" than submitting two math scores and one in physics or two language scores plus English lit. You get the idea?
You can only take three SAT II tests during each test administration, but there is no limit to the number you can take overall. While colleges do pay the closest attention to your three best scores, they will see all of them, so if you are able to do well in a variety of areas, it can certainly boost your chances at decision time.