I think that Giant Pandas would be a step in the wrong direction for Chester Zoo. For the most part, I get the impression that imports at Chester are done with conservation in mind; seeing as the Giant Panda has already benefited massively from conservation initiatives, working with species that have not been such fortunate would be a better decision for Chester to make. While the above statement is quite subjective, all things considered, I don't really want to see pandas at Chester any time soon.
Gorillas would be great (and are most likely going to arrive in future developments), but they are not a priority for me seeing as Chester already holds three species of great ape. Pinnipeds would be a great addition to Chester, but not a California Sea Lion. The species is already held at 14 zoos, several of which (Colchester, Blackpool and Yorkshire to name a few) have provided excellent enclosures for the species, and it is Least Concern in the wild.
So at the end of the day, it came down to Polar Bear or Hippopotamus. Both are Vulnerable in the wild and decently rare in UK zoos, although in both cases the polar bears are more so. I would love to see both species as Chester, but if I had to pick one, it would probably be the Hippopotamus, as I feel as though Chester could do a lot with the species; they have the money for underwater viewing, a feature sadly lacking in the British Isles, and a good indoor area. And does Chester really need three species of bear? Overall, as tempting as it is to vote for Polar Bears, I have decided upon the Hippopotamus.