Figure of merit (FOM, defined in Sect. 6.1) as a function of the transverse extinction optical depth of our slab model, τ_ext = 0. 1, 0. 2, 0. 5, 1, 2, 3, 5, 8, 10. The simulations were run on a basic multi-core desktop computer. A higher FOM value indicates a more efficient algorithm. Results are given for several variants of the photon packet life cycle (PLC): colours indicate without (orange) or with (green) forced scattering, or with forced scattering and also recording the radiation field (blue). The three panels correspond to different values of the scattering albedo. The left panel (ω = 0.9) represents the strong scattering regime and is applicable to dust attenuation at UV wavelengths. The central panel (ω = 0.5) corresponds to a situation where absorption and scattering are equally important and corresponds, for example, to dust attenuation at optical wavelengths. The right panel (ω = 0.1) corresponds to weak scattering, as applicable to dust attenuation at infrared wavelengths or radiative transfer in molecular and atomic lines. Line styles indicate without (solid) or with (dashed) explicit absorption. Error bars indicate the estimated uncertainty on the FOM values caused by the remaining Monte Carlo noise in the converged simulations.