The type of heater best suited for an application involves the dynamic of the process, space limitations, available electrical or gas supply, cost and appearance among other considerations.
There could be several acceptable solutions for a single application. For example: water in a tank could be heated by direct immersion, clamped-on strip-, tubular- or band heaters around the tank or even radiant heating elements.
These conduction installation options are listed in the order of most effective heat transfer from the heat element to the part. It is not necessarily in order of the most economic way to heat up a part.