Here are some links and attached old articles and other more recent that prove APSIM is currently the tool to give the best results in the field of agriculture.
- The APSIM Model – An Overview (PDF Download Available)
I don't think that it is necessarily the best under all circumstances, but it is a good tool that is constantly improving due to a good development group. Also, it has had significant development for tropical countries under nutrient limited conditions, so it is a good option for such situations.