Mini-grids are well known to be a suitable solution to foster rural electrification in developing countries, and yet risks and high costs are hampering their spreading. Even though effective tools can help developers to identify the optimal design and operation of a mini-grid, no standard approach have emerged yet. This paper proposes a numerical comparison among deterministic methodologies to optimize a rural minigrid considering the effect of different operating strategies. The typical load-following and cycle-charging strategies are compared to predictive approaches, as rolling-horizon and a one-shot model, which optimizes both the design and operation together. The two latter models allow achieving additional savings compared to traditional operating strategies, but the computational requirements increase sharply. Results suggest that sizing methodologies using load-following or cycle-charging strategies are more suitable for preliminary design, while predictive approaches should be used for the fine tuning of the size of components. This study can provide guidance on design and operating methodologies for rural mini-grids in developing countries.