As a former subscriber to both, Scout has a good-ol-boy network going on, where only a handful of mods know the info, but they don't actually share it with the people who pay to know the information. The articles leave a lot to be desired and when they do share inside information, it's limited. Usually another site will eventually break the news and the guys at Scout say "We were bound by secrecy by our source." Of course, I canceled my subscription a few years ago. It may have changed since then but I doubt it.
Rivals has better information, but I recently canceled there too. A friend of mine, who's mainly a lurker on GT message boards also recently canceled his Rivals membership. It was a great site up until about a year ago, when posts on message boards starting to get deleted just because the mods didn't agree with what was being said. I also canceled because it seemed like the content was beginning to suffer.
If I had to choose one, I would say Rivals. But if I were you, I'd save the $10 a month and just wait the 20 minutes to an hour for private message board stuff to go public.