What is the purpose and use for the porch? Porches generally provide weather protection, shading and reduce the opportunity (or at least intensity) for interior natural lighting. Thus one has to consider a porch as just another part of the house design to best locate not only for it's purposed purpose, but also for the other effects a porch creates.
There is no universal strategy for porches (locate on the south and east...) any more than there is a universal strategy for location of kitchen, garage, or any other interior space.
Location is really a climatic and weather-related issue, based on one's geographical location. Generally speaking, a southern exposure is the preferred house orientation, particularly for passive solar design strategies. This is because at mid-day, the sun is always due south. In the summer the sun is highest and can be moderated by use of overhangs, trellis elements and the like, in order to prevent direct sunlight from entering the house. Proper overhang depends on latitude, but generally in the middle U.S. something on the order of 6' of so tends to work. There are tons of charts which give sun angles at different latitudes at different times of day in different seasons to use for reference in design.
In the winter, the sun is lowest and the same overhangs, trellis elements, etc. can also be designed in such a way as to allow direct sunlight into the house for lighting and passive heating.
Continuing this analysis, west and east are the most problematic orientations since the sun will be so low that it is impossible to defeat or mitigate at some point in time. It's harder to generalize about the north side of a house, but often north and west are the directions of winter storms and severe weather (one needs to carefully check their own prevailing patterns based on the micro-climate for each specific site). Thus, north and west will often be good opportunities for porches for the purpose of weather protected entries and exterior access.
Said differently, for passive energy strategies the best house orientation is to the south, with the longest portions of the house facing south and north; shortest portions of the house facing east and west. This is why it's common for architects to locate the major interior living spaces to the south, to maximize windows on the south and to minimize them on the north, at least in preliminary design studies.
This strategy is also one of the best for analyzing land and lots for possible purchase and building. Level or down-sloping land where the entrance is on the north side and the views are to the south often may be best for building and outdoor usage, if all other considerations are equal.
Hope this helps.
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