The photos I've seen of Frankfurt's generally make it look architecturally at least, more attractive and stylish than Leipzig's, which has the 'grotto' effect in the outside enclosures, which I don't like.
The orang-utan enclosure is definetely better than the one at Leipzig.
The outside enclosures at Pongoland are the best I have ever seen, only Apenheul is giving their bonobos and gorillas comparable high grade outdoor enclosures.