The person who can take the LSAT without preparation and do well are few and far between. No one advises students to take that route. But after that, there isn't a lot of consensus among pre-law advisors. Here's my suggestion. You have to take a deep and honest look at yourself. Can you work on your own, be self-directed, and disciplined. If so, you can buy preparation books and work steadily. The key is to understand the logic of each section of the test and then practice, practice, practice. If you work on your own, you can find excellent books on the NAPLA resource page. These are books prepared by LSAC which analyze the test and then provide multiple practice tests. Keep practicing. There are other books which work well as well.
If you believe that you need more guidance and discipline imposed by outsiders (and note I am adding guidance here) there are two main groups people use. Kaplan and Princeton are the biggest and most expensive. You will find many who went through this and found professional preparation essential. An on-line program is Test Sherpa (link) I don't know anything about its results.