It has long been understood that from a standpoint of energy use, the two best orbits for a high orbit space station are the L4 and L5 Langrangian points, which are actually on the moon's orbit 60° ahead and behind it.
While these two orbits are almost infinitely stable, by virtue of being at the moon's orbit they require about the same amount of energy to reach as the moon does. This immediately lowers the desirability of these orbits. Also, by being at that distance a space station spends almost no time in the earth's shadow, which effectively doubles the amount of solar radiation received in a given period of time over that of the same space station in low earth orbit. For these and other reasons, a moderately sized space station in low earth orbit is probably the best, at least at this point in our technological development.
Pictured above is Space Station V from the movie 2001, a Space Odyssey. Like much of the movie, Kubrick's version of Clarke's vision gets most of the science mostly right. SS5 is toroidal to allow for centripetal "force" to function as an artificial gravity. As such, it is the only one of our candidates which can reasonably approximate earth's gravity; all of the rest will have significantly less gravity than we are accustomed to.
SS5's toroids are individually relatively small and modular, making it easier to build in stages while utilizing the stages which are already completed. We see this in the movie; one module is fully functional while the other is still under construction. Unlike a colony on Mars or one of the moons, all of the resources to build a space station like this would need to come from earth. However, we have already established the protocols for doing so with the existing International Space Station. It is also possible that instead of a true toroid, we could build a segmented toroid out of spent liquid fuel tanks of rockets which are already being put into low orbit for other purposes. A version of this technique was first envisioned by Wernher von Braun in his original proposals for what eventually became Skylab.
A space station like SS5 could support a significantly large number of colonists in close enough contact with earth to make regular commerce between earth and the station economically feasible. Said commerce would eliminate the need for complete independence from earth during the critical first stages of colonization. In almost every respect this would be the easiest of the four proposed attempts at outward colonization to achieve. The lessons already learned from ISS, Skylab, Mir, Almaz and Salyut will prove invaluable, and a toroidal station will have the significant advantage over all of these of not having to contend with the long-term effects of microgravity on the human body.
The biggest disadvantage from the standpoint of species survival is its biggest advantage form every other standpoint -- the ease and frequency of physical contact with earth. If earth's human population were severely threatened with extinction by infectious disease, in all likelihood a low orbital station, with its frequent exposure to terrestrial humans, would succumb as well. For most other scenarios, a thriving colony in low earth orbit could very well mean the difference between survival and extinction of the species.
I would, however, probably opt out of the ugly red chairs.
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