I have to go along with Marty on this one....in the case of twins, you have to install two of everything...two fuel systems, two ecu's, two shut off valves, two battery packs. In other words there are twice as many components, and twice as many components to fail. As an example if the weakest component had MBF of say 1000 cycles, this will be reduced to 500 cycles (approximately) because 2 of them are being used on each flight.

Turbines are utterly reliable as long as they have fuel, no air bubbles, and the ecu keeps ticking. If reliability were the determining factor, a single turbine with a bullet proof system installation would be the way to go (IMO).

However, for separated engines -SU-27, A-10 - etc, twins would be the way to go. Twins also win in the way-cool category as well........