Use FAQPage schema when your site publishes an official multi-question answer page authored by your team, and use QAPage when the page is a single user-submitted question with community-submitted answers — Google's structured-data guides define the two types precisely and enforce the distinction.
FAQPage documentation: a list of Question/Answer pairs authored by the site itself. The type is best-fit for support docs, product FAQs, and educational hubs.
QAPage documentation: a single user-submitted question with one or more community-submitted answers, an accepted answer, and optional suggested answers. Best-fit for forums, community Q&A, and knowledge exchange sites.
Both require answerCount on their Question nodes — a validation failure Google is known to flag. Both are eligible for a rich-result treatment (though FAQ rich results have had visibility constraints in the past; publishers should not deploy either purely for guaranteed visual placement).
The wrong-shape failure mode: an author-written FAQ marked as QAPage validates in the Rich Results Test but misrepresents the page. Match the type to the page's real editorial structure.
For answer engines the practical difference is small — both make the answer text and question text explicit — but honesty matters. Use the type that matches your content.