AGAST vs FAST evaluation
I am not aware of a direct comparison, other than the agast paper:
http://www6.in.tum.de/Main/Publications/Mair2010c.pdf

However, Agast is also based on AST, which is developed by the authors of FAST -Edward Rosten (et al.). It is just a better training. So it might be safe to assume the improvements, based on the original Agast paper.

Moreover, here is a tracker I implemented based on Agast features:

https://www.youtube.com/watch?v=rZWu4LxmsME

This works fairly well in many cases and was able to convince me on the power of Agast (Doesn't work as good with FAST features).