I know that speaking for myself I tend to have relatively balanced functions in most respects, which actually does not make the choice of partner a particularly natural or straightforward one, it mostly boils down to who INTERESTS me or attracts me the most (itself to a large extent a matter of intellectual compatibility). The one conistent factor, therefore, is that I've never been involved with an S type or a J type as far as I know, (except possibly for the latter one mutual crush that didn't lead to much when I was in my teens). Nothing against S types, it simply hasn't worked out that I've met one I've found particularly appealing in that sense.
Unfortunately "Interesting" + xNxP =/= stable personality much of the time!
And I have become so tired of being on the recieving end of stereotypical P-type flakiness and unreliability that I am thinking maybe I would be better off seeking out someone who shows J-ish tendencies of some kind next time round. (Yes, I know this is UNhealthy P-type behaviour, but I really have had a gutsful of it over the last few years, being let down repeatedly at critical times hasn't had a particularly good effect on my life or my appreciation of the relationship potential of the opposite sex...)