HFSS are 3 D EM simulators based upon different computational techniques. HFSS is based on Finite Element Method (FEM) which is more accurate for designing antennas .AWR, i used while simulating different kind of filters but dont know the details of this software.
I have used HFSS. It is popular in electronics industry. It is works well foR 3D/2D EM analysis. AWR is good for RF circuit deisgn (Filters/Osc/plls/etc) but i am not sure about 3D analysis capabilities.
Good thing about AWR they give free license to schools and learners. Not a bad deal to start with.