To be fair, when evaluating Rivals vs Scout, I don't think it is fair to just compare evaluating talent and ranking prospects into the equation.
Site Design/Functionality: This is a huge factor to me, and Rivals wins this matchup hands down. I feel like I'm stuck in the mid 90s whenever I hit up the Scout websites, from the design, to the layouts used, to the backwards message boards system. On top of it, some of their internal sites (Scout Combines, for instance) are horrible to look at... go check it out just to experience that visual eyesore. Rivals sites tend to be more visually appealing, the layout is smoother and just easier to use.
Winner: Rivals
Writing (Content and Depth): While this can really vary from site-to-site within the brands, I'll only look at the Notre Dame versions. That said, Scout blows Rivals out of the water. The articles on Scout are more in-depth and you really get to know more about the recruit whereas Rivals seems to have a skeleton framework they write from. Also, the replication of articles on Rivals is pitifully slow and sometimes the content is aged so much that it is no longer relevant.
One thing I noticed about both organizations that is troubling is the accuracy of offers. There have been at least 5 (this year) or so occurences where players were listed with a scholarship offer from Notre Dame only to find out that they did not have one. Oops.
Winner: Scout
Multimedia (Pictures and Video): Rivals takes this one... by a landslide. The video production on Rivals is much more clean and I find the video on Scout to be downright awful to watch sometimes. Rivals does get pretty bad occasionally, too. Where Rivals really wipes Scout up is in the AMP footage, which is always well done and timely. For as much as these companies charge it's members, the video should be crystal clear and they should have multiple images on all recruits... there really is no excuse.
Winner: Rivals
Talent Evaluation: I don't really think you can claim one organization is better than another in this area because talent evaluation is very subjective and in the end, it's just the opinion of a couple people. That said, you can definitely see regional/school biases coming through in rankings.
Rivals, based in the South, tends to heavily favor Southern talent. I believe just over 1/3 of the Rivals 100 came from Florida, Texas and California, and a majority of the players come from the South overall. Scout, on the other hand, tends to have a more balanced approach, with top recruits from all over the map. However, Scout seems to upgrade/downgrade players more on where they seem to verbal too, which I find absolutely ridiculous as well as downgrading players that suffered injury without seeing how they recovered first.
Winner: Push
Summing it all up, Rivals is the better service if you are wanting to see the multimedia aspect of recruiting (video, images) whereas Scout seems to be better if you want to read in-depth reporting, feature articles on recruiting.