Of course, what we need to know is what is more common, habitable terrestrial planets that are around the size of the Earth, or ones that are larger. At present we are finding large planets because our detection methods are not sensitive enough -yet- to discover smaller ones. But that is rapidly changing. But even Earth sized and larger sized terrestrial planets are both just as common, the fact that life may be more likely to arise and/or survive on the larger ones than the smaller ones may still indicate that alien life will tend to come more from the larger terrestrial planets.
The main reason why larger terrestrial planets would be more conducive for creating life is that they would be more geographically active:
Plate tectonics are crucial to a planet's habitability because they enable complex chemistry and recycle substances like carbon dioxide, which acts as a thermostat and keeps Earth balmy.A larger planet is more likely to have the complex chemistry necessary for life to begin and would have a more active recycling of substances like carbon dioxide, among others, which helps to keep the climate more stable (overall). In addition, a larger planet would have, probably, a thicker atmosphere, which would offer more protection from meteor impacts. If a larger active terrestrial planet also has a stronger magnetic field, then it would have increased protection from cosmic radiation. Such a planet would be a safer, for a longer period, environment for life to begin, evolve, and thrive on.
The next question, to be addressed later (I have papers to grade at the moment), is how would a larger planet affect the development of alien sentient beings?
Harvard-Smithsonian Center for Astrophysics. "Earth: A Borderline Planet For Life?." ScienceDaily. 14 January 2008. 11 February 2008.