"BA is the most well-known, but Baseball HQ is at least five steps ahead of BA on intelligence with prospect evals."
BA is about 75% scouting, 25% stats - and their reputation has earned them significant intel with scouts and teams that we do not have access to.
Baseball HQ is 100% stats. I'd agree that stats are frequently more accurate predictors than scouting, but at the same time I don't see many profound prospect analyses coming off of that site that you or I would be incapable of ourselves.
Baseball HQ has very little to tell you right now about a Jameson Taillon that you don't already know, or could not deduce yourself. BA will literally be coming out with a book. There's very few lasting prospect resources out there, and none of them with the history, organization, and resources of BA.
Baseball America can tell you, today, where all of the 2010 draft picks and international amateur signings rank among the top prospects in baseball. This will not only be consistent with how the players are viewed by scouts/teams, it's based on input directly from them. Yes, five years from now a large number of those rankings will be wrong. That doesn't mean the information does not have value today.