To maximize muscle building pay attention to the cadence of your reps.
A lot of us take rep speed for granted, but what you should know is that it matters how fast you perform each rep, and even how fast you perform each segment of a rep. For example, speed builds explosive power while slow builds strength. The difference can be seen in the way powerlifters train as opposed to Olympic weightlifters.
Powerlifters perform slow, deliberate reps and build great strength as a result whereas weightlifters train faster, giving them the explosiveness required to hoist heavy weights overhead.
For the average trainer a combination of the two works best. I recommend going quicker on the positive portion of the movement, without jerking or throwing the weight, and letting it down more slowly. This gives you the best of both worlds – strength and power, and an ideal muscle-building environment to boot.