Neither. If you want to learn an effective way to write exams, spend the $150 for LEEWS and do it over the summer. Although I don't recommend it, you can spend $20-30 and get some used Examples and Explanations on Ebay or Half.com to get familiar with some of the terminology you'll see. Don't try to memorize though, as you don't know what you're prof will cover, and memorization isn't really the point, unless you have closed book exams (and even then, you don't start memorizing until a few weeks before finals)
I did what I recommended above last summer. I flipped through the Torts E&E, but soon got side tracked with hanging out, relaxing, and moving to a new city. I did LEEWS in late September/early October.
The bottom line, however,is that nothing is really necessary for anyone; do what works for you. But I strongly feel that Law Preview is not necessary, and you can get the same information on your own for MUCH cheaper. Law Preview exists solely to take advantage of 0L's insecurities.