object and question solved by HFSS? CST?

Compared with CST,
what kind of object is suitable for being simulated by HFSS?
what kind of question is suitable for being simulated by HFSS?

Compared with HFSS,
what kind of object is suitable for being simulated by CST?
what kind of question is suitable for being simulated by CST?



Added after 23 minutes:

Which one should I trust?

e.g.
1. s-parameter of via stub.
2. s-parameter of connector transision region.

etc...

Added after 3 minutes:

basically, what kind of object and question is suitable for FDTD? and FEM?