Halotestin is extremely ANDROGENIC but will NOT create a lot of anabolism at all. It will not produce muscle-mass, just massive strength.
As for Primobolan, it is indeed very anabolic, and will thus maintain muscle mass while dieting better than almost any other steroid. However, lacking any appreciable androgenic component, it will fail to build a lot of muscle mass by itself.
Anyway, Trenbolone is the most anabolic steroid(and the most androgenic), and will build the most muscle mass by far.