If the former, it is probably a draw for me, or with ZSL just edging it.
As is probably obvious from the way I have voted, I would tend to disagree with you that ZSL deserves the edge in this one

for the sake of transparency, my thought process is as follows:
Collection:
RZSS has a total of 22 carnivoran species, to the 15 held at ZSL; this is despite the fact that (as I have openly bemoaned for many years) the former has undergone a comprehensive programme of getting rid of the greater part of their previously-excellent collection of carnivorous oddities, often on the grounds that they weren't deemed "showy" enough to be worth keeping. There is a reasonable amount of overlap between the species kept at ZSL and those kept at RZSS too, with only six of the species held at ZSL being unique to that organisation within this match. Of the unique species which *are* held by ZSL, one has been actively mismanaged into (near) extinction over the last few decades and represents a massive waste of potential - the Sri Lankan Sloth Bear - whilst another is on the anti-invasive list and as such will soon be gone from the collection. The presence of Narrow-striped Boky is more or less the only thing of note ZSL has to offer in this regard.
Exhibitry:
First things first..... Highland Wildlife Park has some of the best carnivore exhibits in Europe - especially where the Snow Leopard, Polar Bear, Eurasian Wolf and Amur Tiger are concerned - with the bear exhibit being *
the* best I have seen for the species full stop, and the snow leopard exhibit close to this. The remaining exhibits at this collection all reach pretty high standards, with no low points. Over at Edinburgh, despite the aforementioned winding-down of the carnivore collection the remaining exhibits are still quite good, with particularly good showings for the Asiatic Lion, Sumatran Tiger and Sun Bear enclosures - the new Giant Panda exhibit is also pretty good and significantly larger than the old exhibit, even if I personally think it is located in a position a shade too exposed to the elements. None of the exhibits at either collection fall foul of the temptation towards overtheming or ill-advised attempts at "immersion" by filling the majority of the available space with mock rock, market stalls and suchlike, with the actual animal enclosures an afterthought.
Conversely, the majority of the carnivore exhibits at London are either unremarkable, or horribly overthemed messes of the sort I mention above

the exhibits at Whipsnade are somewhat better, but I would suggest only the Wolverine and Cheetah exhibits stand out.
Conservation:
Both organisations pull their weight pretty well in the realm of in-situ conservation as a whole, but where carnivores are concerned I think that RZSS has the definite edge when it comes to conservation work, given the fact that both collections are heavily involved in the Scottish Wildcat programme, both in terms of captive breeding, genetic testing and reintroduction, whilst HWP has a large and extensive off-show breeding facility for Amur Leopard which is specifically designed to minimise the human contact of any cubs born, allowing them to be reintroduced into the wild with the highest possible chance of success. ZSL, although having involvement in many relevant in-situ programmes itself, doesn't really have much to offer where ex-situ work, and work on carnivore populations closer to home, is concerned.
It must, however, be said that this *is* the area in which ZSL shines the most, even if I still think RZSS beats it here.
Overall Management:
To be honest, I think that the recent history of the carnivore collections at *both* organisations displays a certain level of mismanagement and decline - for RZSS, the drain on finances and resulting loss of much of the prior carnivore diversity which the Giant Panda loan has caused; for ZSL the long slow decline of the carnivore collection, over-themed exhibit complexes for lions and tigers which are "all fur coat and no knickers" as it were and take up massive swathes of space which could have been used for better purposes, and much that is lost not being replaced. However, RZSS has displayed *some* bright points in the last decade along with the low points - the development of not one but two exceptionally good polar bear exhibits and the successful breeding of this species, the construction of the off-show breeding facility for Amur Leopard, construction of several other new exhibits which all reach or exceed expectations and potential, and (to be blunt) rather more breeding success across the board than has been seen at ZSL
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With this all said, I was torn between a 3-0 vote for RZSS, and going 2-1 in light of those strengths which ZSL does display.... but ultimately, a few things swayed me towards the former:
- Despite the decline of the carnivore collection at RZSS over the last decade, there are enough bright points that I see a chance for this decline to be reversed in time; I am somewhat more pessimistic in this regard where ZSL is concerned.
- ZSL is responsible for the construction of Land of the Lions and Tiger Territory in the last decade

- RZSS has the polar bear exhibit, amur leopard exhibit and snow leopard exhibit up its sleeve.
- Basically, ZSL demonstrates so much more wasted potential than does RZSS. It *should* be the best zoo organisation in the country, in charge of the best zoos in the country.... but it doesn't come close, either in terms of carnivores or as a whole

I think that a 2-1 vote for RZSS is entirely acceptable and possibly the best option for most people voting, as seems to be the case looking at the votes right now, and I acknowledge that my sheer love for the carnivore high points at HWP may well influence my feelings in this regard (although I hope the amount of criticism I have levelled at RZSS over the last few years demonstrates I am not overly biased towards the collection).... but I think I have demonstrated why a 2-1 vote for ZSL is definitely *not* justified.