Sadly there is no quick and simple answer to the question. However hopefully this might help.
Buck converters or buck regulators tend to be more efficient than
Low-dropout liner ones, however that is a bit of a generalisation.
For some applications there is little to choose between them. For example a typical
LM2596 design will theoretically be 95% efficient, but only when the input and output voltages are relatively high (see efficiency, fig 5 page 6). If however we run it with low input and output voltages, its efficiency may be much lower (<70% for 5V input and 3.7V output). This does not mean they are a bad choice for this application, as simple linear regulators are often much worse in terms of simple efficiency.
Both types of regulator have their advantages and disadvantages.
One of the typical applications of these cheap LM2596 regulator modules is as a solar regulator, where the somewhat variable output of a solar panel array (with a nominal output voltage of perhaps 24V ) is used to charge a 12V sealed lead acid battery. In this application, you could expect 90% plus efficiency, with little energy wasted as heat.
Running a 3.7V camera directly from the LM2596 might not be so effective as the output voltage is relatively low, so we might waste a bit more power. The most efficient solution would be to run the camera directly from a large 3.7V LiPo... however high capacity 3.7V LiPo/LiIon batteries are few and far between (and thus expensive). Therefore we will need to compromise between efficiency and utility. It is much easier to find a high capacity battery of say 12V (a sealed lead acid or SLA) or 7.2V (a RC modelling racing pack) and then attach a cheap regulator (and waste a little of our precious capacity), than to find a perfect 3.7V source.
