Yeah, a standby would be too stressed. A prime power is probably more correct. At the link I gave, go to the "Cat Brand Generator Sets Rating Guide" and on page 10 of the pdf there is a description of gen-set rating types.
Reciprocating piston engines, generally, are more thermally efficient. Gas Turbines are more compact; they can only achieve greater efficiency by using a combined cycle where steam is used as a bottom cycle recovering the heat from the turbine's exhaust stream. As a combined cycle, they become much more expensive.
The diesel cycle depends on the compression of the fluid to ignite fuel as it is injected. Compressing a fluid greatly increases its temp to make conditions right for ignition. Low weight hydrocarbons (gasolines down to NG) at these conditions would cause detonation. Heavy weight hydrocarbons, like diesel up to heavy oil, burn more slowly and more controlled.
Diesel engines in gensets are often offered in NG versions. (In simplified explanation) This is done by lowering the compression ratio and changing to a carburatted intake air (in other words, fuel injected into the intake of the engine rather than direct injection near TDC in a diesel.) The diesel injector is then replaced with a spark plug. Converting a diesel down to a NG version is great because NG has less energy; which means less stress, less heat load, and also has no heavy soot load.
