This is an interesting match-up, because it’s very category-dependent. Barcelona would have romped home on ectotherms, Attica on ungulates or birds, and Lisbon on primates. Only carnivores and miscellaneous mammals are potentially difficult choices. Unfortunately, Barcelona’s carnivore collection is nondescript both in species and display quality, but both Lisbon and Attica have claims here.
Lisbon’s ace in the hole is the Iberian lynx, and the enclosure is generous in size and full of natural features. It’s great, except that I doubt many people have more luck in seeing an Iberian lynx than I did. Lisbon is otherwise pretty ABC-ish, from memory, which doesn’t bother me but will some people. What *does* bother me a little is that many of the ABC exhibits, including for lions and bears, were overstocked. There were about 13 lions in a reasonable but not generous-sized exhibit. I think there were five brown bears, too. Lintworm has identified the issue with the tigers.
Attica is pretty strong on carnivores too, with a more or less complete set of ABCs, though not so many rarities (unless the occasional rescued Mediterranean monk seal, which I didn’t see, counts). I was impressed by the big cat enclosures, especially for lions, which at the time of my visit in late May 2017 were the best I’d seen in Europe (I visited Lisbon in mid-March and Barcelona in very early April, from memory). They did fall down the rankings as I made my way through Germany, the Netherlands and UK, but better than Lisbon and Barcelona. The vegetation is the same low shrubs and grasses that occur throughout the zoo and, indeed, throughout Attica, and I always like a zoo that sits well within its environment.
My vote is sitting with Attica.
Barcelona doesn't seem to keep its carnivores in decent enclosures either, and Attica appear to have nice enclosures for tigers and cheetahs but if only they had monk seals on-show at all times then that would trump the lynx.
