No preference whatsoever.
Well, admittedly, some admission officials (whether they’ll say so or not) bring their own prejudices to the committee-room table. This applies to everything from favorite band instruments to favorite sports to political or even religious views, and it may occasionally apply to seemingly comparable curricular options as well.
But when it comes to considering one approach (IB or AP) more rigorous and/or desirable than the other, most admission officials are neutral.
One warning, however, is that not all AP classes are created equal. In the eyes of admission folks … at least at the snootier schools … some AP classes such as psych, art, and econ aren’t valued as highly as the sciences or calculus. Even AP Stats (which my own son is taking right now) is considered something of a poor-relation in the AP world. I personally feel that it’s a very valuable class, especially for students who go on to major in fields such as business or psychology. And certainly many math teachers have argued the same. But, even so, like Rodney Dangerfield, AP Stats doesn’t get a whole ton of respect from many admission officers (except perhaps those who took it themselves and know better).
So an applicant who has pursued an AP program that is top-heavy with the more “lightweight” AP classes would probably take a back seat to a candidate doing the full IB diploma. But, in most cases, it doesn’t matter which route a student follows as long as he or she has successfully taken on academic challenges.
But, since you were speaking of “constant change,” you should also keep in mind that some colleges seem to periodically revise their policies on credits awarded for AP and IB exam results. So this is one area where one program might trump the other at a particular institution. However, because most students who have a choice between AP and IB make their decision long before they know which college they’ll attend, and because these colleges do amend their policies from time to time, it probably makes little sense to plot the academic course of a 14-year-old based on how many college credits might be awarded down the road.
The vast majority of high school students don’t get the AP vs. IB choice anyway. But, for those who do, personal preference and logistics (e.g., attending the nearby high school with busing and not the more distant one without it) should rule the day.