Rockwool cubes are super simple and super reliable too, just keep them damp, not wet.
I agree with Benzels, always plant more seeds than you need, that way you can pick the healthiest ones; and not all seed germinate either.
I generally plant two fem seeds for each fem plant I want and 6-9 regular seeds for each regular plant I want.
This way you only grow the best examples of each strain and with the regulars, out of 6 or 9 seedlings, your chances of picking a "female looking" one is greatest.