Natural Merchants was king in SE3, but ever since SE4, it has been worth very little in stock. 3 turns to build and a tiny fraction of system facility space is a trivial gain for the points that could have gone towards Advanced Storage Techniques, Hardy Industrialists, tech traits, etc.
This was for SE4, but the same principles remain (other than experience-related stuff, which is now possibly worth less than Natural Merchants due to the low cap of bonuses from experience).