  When engineering microscopic machines, increasing efficiency can often come
at a price of reduced reliability due to the impact of stochastic fluctuations.
Here we develop a general method for performing multi-objective optimisation of
efficiency and work fluctuations in thermal machines operating close to
equilibrium in either the classical or quantum regime. Our method utilises
techniques from thermodynamic geometry, whereby we match optimal solutions to
protocols parameterised by their thermodynamic length. We characterise the
optimal protocols for continuous-variable Gaussian machines, which form a
crucial class in the study of thermodynamics for microscopic systems.
