Instead of looking at which named function is preferred, I thought perhaps to look at whether the base of creative functions are preferred (base subtype and creative subtype as opposed to something like intuitive subtype). A lot of this may just end up broken as I've seen very little information of subtypes, so a lot of this is just guessing and filling in gaps with possibilities.
The base function is the ego function through which a person primarily takes in and understands "his world". It is the method he chooses to initially take in information, before consciously manipulating it in any manner.
The creative function is the ego function by which thoughts and actions are realized and communicated. Such thoughts and actions are based upon the information as it was taken in by the base function, hence why types in a look-a-like pair (two types who share the same creative function) will realize in a similar manner, however they realize different things as the information they work from was perceived in different manners.
A base subtype would (in theory) prefer to focus more on taking in information from the outside world. A creative subtype would prefer to make use of the information already taken in. There would not appear to be much difference between the two subtypes of a given type, as they both still take in information the same way and act upon it the same way. A creative subtype might superficially look something like its mirror partner.
Subtype could be either inborn or cultivated by the environment. Either way, it's possible that the subtype is more of a continuum than a discrete definition. One would likely fall somewhere between base subtype and creative subtype, depending on how he balances taking information in and acting on it.
I'm starting to think subtypes might be an effort to make socionics explain more of the personality than socionics is capable of explaining.
Any thoughts, additions, or corrections?