CST MWS or HFSS for planar structure..

from CST MWS and HFSS, which tool is better for full wave simulation of a planar structure ?

debating "better" just starts a never ending street fight. I think of this as a "Good, Fast, Cheap" ....... pick any two debate, The "better" software is the one you have and know how to operate.

according to my experience HFSS is better in speed than CST MWS when simulating planar structures.

I agree. I use HFSS and I am getting pretty good results compared to measurements for planar antennas.
I think CST/SEMCAD is better when your structure is electrically large since FDTD (CST,SEMCAD) does not require as much RAM as FEM (HFSS).
Adel