Which habitable zones have the most real estate?

Over the last few years, our concept of a habitable world has become much broader. Besides terrestrial planets in the conventional habitable zone roughly 0.7-1.5 AU from a Sun-like star, we realize that a moon of a Jovian planet in the habitable zone may be habitable, as well as a moon like Europa that is tidally heated. Habitable planets may exist in eccentric orbits and in multiple-star systems. Even tidally-locked planets may have habitable regions near their terminators. All of this provides a potentially rich variety and diversity of habitable planets. But the total number and relative importance of all of these types of planets remains relatively unexplored. Which of these zones have the most real estate? In this paper, we estimate the total habitable surface area of all the potentially habitable worlds in the Galaxy and distribution of this surface area among the various kinds of habitable zones described above. For each type of habitable world, we estimate the mean habitable surface area per body and the mean number of bodies per spectral type and class of star. For each case we attempt to apply relevant numbers from the solar system, and then we add detail from the growing literature on extrasolar planet distributions as a function of radius, mass, metalicity, etc.. Estimates like these may ultimately help us understand probabilistically the origin of life and prioritize our searches for life elsewhere.