What considerations are made in determining whether to use a sand bath or oil bath?
The following is the comparison list from the top of my head:


Oil for the oil bath is often available commercially, every batch has the same properties and is arguably easier to store and transport; sand bath requires sifted and refined sand (quartz sand, ideally). It all depends on what's easier to find a good supplier and storage for.
Oil bath heats up relatively quickly, especially if the oils isn't very viscous; sand bath heats up very slowly due to slow heat transfer in powdered/granulated material.
As a consequence of the former statement, oil bath is uniformly heated, whereas sand bath always has a temperature gradient with the maximum temperature at the bottom and minimum on top layer.
This requires that the tip of the thermal sensor is located at the same depth as chemicals in the reactor.
Oil bath can usually only be heated up to approx. 250 °C max depending on the oil used; sand bath can be heated up to 400 °C (provided a ceramic pod is used).
When operated at high temperatures, mineral oil in the oil bath may start to decompose producing volatile health hazardous organics; sand bath, if the sand was prepared correctly, doesn't deteriorate even at high temperatures.
Silicone oil is much safer in this regard, but is also considerably more expensive than mineral oil.
In case of temperature control fail, oil bath may even ignite (again, depends on oil used); whereas sand bath will just overheat – however, the aftermath may be comparable.
Oil bath can be used with rotavap; sand bath can't.