An interesting topic, Luis.
There are themes which strongly attract me (i.e. fire and rescue), themes which attract me because they can be used in conjunction with fire and rescue (e.g farm, city life, trains and even the Victorian theme - I still regret not buying both, or even one, of two original Victorian mansions which were going for £60 instead of £120. Now those would have been great for a multi-pump fire!), themes which I find attractive because of past interests (e.g. the knights theme but not some of the recent additions, although things do seem to be getting better again) and then there are the dragon knights, ghost pirates and top agents which I wouldn't give house room to as they are just not the quality of concept I expect of Playmobil and look, to me, cheap and tacky.