ESPN has a unique set up, but I feel they are the poorest of the 3 major ratings sites (ESPN, Rivals, Scout) at evaluating talent. They overrate size and underrate a player's ability to translate his game to the next level. For example, all 4 four of the MVC recruits that are listed as 3* on ESPN (89-91) are 6'6 or taller.And as for which rankings system I use...I tend to follow all of them from a distance, but I really think ESPN has done a great job improving theirs. I like the numerical system as compared to the stars. Stars tend to be more telling of offers, and no one knows if they have been seen. The numerical system seems to give some legitimacy to whether or not the athlete has been seen. What system do you like to use/follow?
To be honest, I don't think there is a 'best' option. I believe Rivals to have the best evaluations, but they evaluate a small number of players. ESPN evaluates a ton of players, but their ratings are rarely congruent with what the majority of evaluators believe. Maybe ESPN is a step ahead, or maybe they're just throwing stuff up there and hoping it sticks.
My best advice? Find a train, plane, or automobile, and go watch these kids play yourself. Take it all in (the good and the bad), and make your best evaulation. Your guess is as good as any!