My sophomore and junior years I scored 184 and 199 respectively. The first time I took the SAT and ACT I scored 2080 and 33.
Personally, I like the ACT better, but I would recommend taking both tests. I recently took both tests again, and I feel much better about my scores this time. However, I will not know my scores for two more weeks.
After studying from many different books, I would recommend Barron's. They have two very well written books, SAT 2400: Aiming for the Perfect Score and ACT 36: Aiming for the Perfect Score, that introduce test-taking strategies for students who are seeking high scores. These were my favorite study guides, but Princeton Review also makes some good books.
My suggestion: get some books or take a class. You have over a year and a half to study, don't waste it. Your scores are already higher than most, but when applying to the Service Academies you will find that most people have high scores too. By studying hard you can raise your score significantly; your score on the SAT and ACT will depend on the amount of work you do now.