I really like this infograph — though take it with a grain of salt. As with many of these thing it can be overkill. Apply what is valuable to you and your industry. If you are a smaller business with limited resources maybe just the Google Analytics or Kissmetrics (which I initially found confusing, but there is value there if you can dig deep) or Unbound which I almost used but wanted more.
But, as usual the best results (a quality lead, not just a form filled out) is with clear educational content.