What is more powerful for micromachined antennas design: HFSS or CST?

I believe CST is the best.

With HFSS you also can get excellent results, but takes much more time the computation effort to solve your problems.

HFSS has a difficult GUI interface, in e.g. drawing a patch takes a lot of time, while in CST just few steps and it is ready.

the CST importation interface (Gerber Multilayer, any 3D CAD) is much more robust that any other software.

CTS also has the PBA (Perfect Boundary Approximation) that reduces any staircase approximation. Other techniques like TST and sub-gridding meshing can be used to improve results and reduce computation effort.

Cheers