I would also recommend Rhinoceros, for these reasons:
1- Great Modelling Core (NURBS)
2- Can model with High precision and ease.
3- Best compatibility with Archicad.
But, then there is the economic issue, if you are going to spend money make it in Rhinoceros, if not, then use Sketchup or use any other software you have in hand.
PD: There are some free 3d CAD modeling software out there but I don't know how good they are for what you need or how compatible with Archicad they might be.