Comment by adrian_b

Gas turbines are more efficient than steam turbines simply because they can be used at higher temperatures.

However the exhaust gas of a gas turbine will still contain a great part of the input energy.

Therefore in order to reach maximum efficiency in a power plant, you must start with a gas turbine, which must be followed by a cascade of 2 or 3 steam turbines that run at lower and lower temperatures (this combination of a gas turbine with some steam turbines is what "combined cycle" means), until you obtain exhaust steam that is not much hotter than ambient temperature, and which can be used for heating, to recover even more of the input energy than what has been converted into electric energy.

Instead of gases or steam, turbines may also use supercritical fluids, e.g. carbon dioxide, which may lead to using less turbine stages and with much smaller turbines (that must work at much higher fluid pressures).

A gas turbine that is used alone, without steam turbines that recover the heat from its exhaust gas, has normally a too low efficiency. Its use can be acceptable only for mobile generators or emergency generators, where the size and complexity are more important than the efficiency.