I've never looked at the Prospectus or Forecaster, so I went out and bought both of them yesterday. My humble opinions after two days reading:Prospectus
has more of a real life feel to it. Often discusses player contract terms and value, which as far as I know have nil fantasy impact. This is what I read to learn more about baseball the game, not the fantasy game.Forecaster
is marketed toward fantasy baseball managers. Heavy on the statistics, light on the summaries. Gives you oodles of metrics which are intended to be used as a tool for making your own forecasts and projects.
Both are very enjoyable reads. Forecaster is heavier on the numbers -- if you don't like math, you might not like this book so much. I think they're both very useful tools for forming your own opinions and I'm glad I got them.