There has thus far been a universal consensus (across both threads) that it's a 2-1 for Plzen. Why is that?
To be honest this is another one where, had a 50/50 option been available, I would have had a little more difficulty in deciding how to vote

but broadly speaking:
1) The various savannah and plains exhibits at Plzen which I have highlighted in past photo compilations (the pair of African hoofstock exhibits and the Indian plains exhibit) are sizable, very pleasant in appearance and (due to a combination of their size, orientation and the position of the public footpaths in relation to the exhibits) the inhabitants are able to escape from public view with relative ease; the single savannah exhibit at Wroclaw is also pretty good, and a decent size, but can more or less be entirely circumnavigated by the public - which on busy days quite possibly has an impact on the animals. The inhabitants are more or less unable to escape from view..... one reason why
@ShonenJake13 was extremely surprised when he revisited the collection with me on my first visit in September 2019, only for us to have no luck whatsoever spotting the last Hartebeest in Europe.
Turned out it had been taken off-show that morning for health reasons, grumblegrumblegrumble
2) The desert houses at both collections are pretty good, but the Sonora House at Plzen (again, extensively discussed by myself previously) has the edge in both exhibit quality and collection scope. Plzen also has the Succulent House, which contains several grassland and desert reptiles, and a rather nice selection of desert and semi-desert adapted plants.
3) On a pure collection level, Plzen is ahead by a LONG shot. Barring the aforementioned Hartebeest, the collection at Wroclaw really doesn't offer anything which isn't already found at Plzen, and as noted above generally in equally-good to slightly better exhibits, whilst Plzen has a lot of big oddities in this regard.
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It is worth noting, incidentally, that neither collection is particularly immersive or themed in this regard.