I like both Baseball America and Sickles.
Sickles got his start working directly for Bill James, so he is a little more focused on the numbers (but takes scouting reports into account as well)
Baseball america is hardly ever wrong when it comes to top hitting prospects (check out their past top 100 lists, they are pretty good at the top), but fall short more often with pitchers, which is just the nature of the beast.
I like to use both because it gives me two prospectives.
"I do not think baseball of today is any better than it was 30 years ago... I still think Radbourne is the greatest of the pitchers." John Sullivan 1914-Old athletes never change.