Having played WHM since early access and now with AST at lvl 60, I could tell you that WHM is much simpler yet powerful. Sometimes simple is good when it comes to healing. AST is no doubt very strong if the cards could be fully utilized. That is IF you could use the cards effectively while keeping the everyone up and dealing with all the mechanics (in A3S). I leveled my AST to level 60 and after a few pulls in A3S, I decided that AST will be my secondary casual class for now and WHM will still be my main healer. Maybe a few months from now once I've played AST enough to become really comfortable with it, then I could try it again for raiding but I feel so much more comfortable and perform much better as a WHM in A3S atm.