I almost feel this question should be "beside testosterone, whats your favorite steroid and why". Just about everyone will say test, because it belongs in just about every cycles no matter what the goals.
But then again, the question seems odd, because your favorite anabolic might COMPLETELY depend what your goals are. I mean, youre not likely going to be running masteron or winstrol if its shear size youre looking for.
...anywho, my answer to the question as it stands is...Testosterone.