These two qualifications look like alternatives and aren't. They're built for different purposes, read by different people, and mean different things — so the question is less which is better than which one the person you're trying to convince actually recognises.
What each one is
AP German Language and Culture is a College Board exam taken mainly by high-school students in North America. It's scored 1 to 5 and its primary function is academic: university admission signalling and, at many institutions, course credit or placement.
Goethe-Zertifikat is an international certificate from the Goethe-Institut, mapped to the CEFR levels A1 to C2. It's taken at any age, it has no school curriculum attached, and it functions as proof of language level — for employers, universities in German-speaking countries, and some immigration and residence processes.
Who should take which
Take AP if you're a high-school student in the North American system. It can earn university credit, it strengthens an application, and it's taught as a course with a teacher and a cohort of classmates.
Take a Goethe certificate if you're an adult, if you need proof of level for a job or a visa, if you're applying to a university in a German-speaking country, or if you're not in school at all. It's also the one that means something internationally — a 5 on the AP exam communicates little to an employer in Hamburg.
Take both if you're a strong AP student heading toward study or work in a German-speaking country. They're complementary rather than redundant.
How they differ in practice
AP is curriculum-shaped: broad themes, a year of coursework, culture woven through the assessment, and an argumentative essay drawing on sources. It assesses what a well-taught course produces.
Goethe is level-shaped: it tests whether you function at a defined CEFR level, independent of how you got there. At several levels the modules can be taken separately, so you can certify reading and listening before speaking.
That modularity is genuinely useful for adults, and it has no equivalent in AP.
Rough equivalences, with a caution
A strong AP performance is often discussed as sitting somewhere around B1 to B2 on the CEFR scale, and a 5 is sometimes mapped higher.
Treat any such mapping as approximate. The exams assess differently, the College Board and the Goethe-Institut aren't measuring the same construct, and no institution is obliged to accept an equivalence. If a specific university or employer matters to you, ask them what they accept rather than relying on a conversion table.
What neither of them is
Proof that you can hold a conversation comfortably. Both include speaking assessment, and both are short, structured and rehearsable. Passing either is a real achievement and it isn't the same as being at ease in the language.
The practical answer
If you're in school, AP, because it's the one in front of you and it's worth credit. If you're an adult with a purpose, Goethe at the level that purpose requires. Decide by audience, not by difficulty.