Well this is another one that Chester has essentially automatically won. I dont know how their indoor area looks (it could be horrible, but this is Chester we are talking about...), but I reckon its outdoor wins it by itself. Nice, if a bit sparse, vegetation, god slopes to imitate the Andean mountain forests, and a good-sized pool fed by a small waterfall, the cherry on top. It is also much larger than the others with the exception of Noah's Ark. the one issue is there isn't enough in terms of climbing opportunities and one could criticise the slight lack in vegetation, but this is a widespread problem across the board in Northern countries.
South Lakes... well.. I guess there's grass
(Is that all the South lakes exhibit or is there more in the line of trees?)
Port Lympne is nice but not enough vegetation and the climbing frames are too small and the exhibit is smaller than Chester. The viewing also seems a bit strange?
Noah's Ark has what seems to be a massive exhibit, but not much vegetation and not much of a slope, but the climbing opportunities are the real problem. However, other than that, it is (almost) on par with Chester, with really nice pool area, some good enrichment areas and good viewing for the visitors. However, the indoor exhibit really lets it down, and the less said about it, the better.
The Jersey exhibit is the best in terms of climbing opportunities except maybe Belfast. The indoor enclosure is however quite small. The Belfast exhibit is similar in some ways, with great climbing opportunities but the exhibit is quite small, depending on where it actually ends, and is probably better than it looks at first glance. It looks quite bleak, but I'm not sure the bears care too much about that. It is a bit too rocky and stony, but overall a good exhibit. However, I reckon Chester has the edge over it and all the others due to just:
that barren and undersized exhibit is not "putting the animals first" in comparison to larger and better-quality exhibits elsewhere!