I would not suggest trying to use a single prep company test to evaluate your level in CR and SC. A lot of company tests provide detailed diagnostic information to test takers, breaking down performance by question type. It's important to recognize that this kind of information becomes increasingly useless the smaller the sample of questions in the breakdown. When you look at your performance, on one test, in CR and SC, you're looking only at a sample of 12-14 questions of each type. There's a huge margin of error when grading a test taker on a sample that small. That's not even to mention the difference in style and logic between prep company questions and official questions, which makes any company verbal score even less meaningful.

Using a GMATPrep test will give you a more reliable indication, but better still would be to do about 25 questions of each type from the beginning of the OG or the VR books. The questions in those books are roughly arranged in increasing difficulty, so by doing the first 25 in each section, you'll be solving questions of similar difficulty, and then you can use your 'hit rate' to compare your ability in each question type. I'd certainly advise working on both, but one other thing to bear in mind is that it tends to be easier to improve in SC with study than in CR or RC, so if your level is similar in SC and CR, you'll likely see a bigger improvement by focusing on SC. Good luck!