An optimize design process of inductors and transformers used in switching power converters is presented in this paper. An analytical modeling of conductor physical behavior was developed to match optimization requirements, and used to compare various components with different cores - coils geometries and wire technologies. Rigorous analytical modeling was applied to achieve minimization of the losses, using homogenization of the stack of wires in equivalent conductive layers of the coils, first introduced by Dowell and improved here. The resolution has been carried out for many different shapes of conductors. All the results are compared to FEM simulations ones and both are analyzed to compare in a quantitative way proximity and skin-depth effects. Then, taking into account the harmonic content of current waveforms, conductor's losses are minimized. It is highlighted that losses could largely be reduced by improvements of coil structure and the choice of conductor's shapes. The benefit of using an optimized design procedure to select best industrial solution has been proven.