I selected Auckland Zoo, as I'm pretty convinced by the reasons which
@Zoofan15 gave, especially when considering the tiger complex in the context of the Wild Indonesia precinct.
That said, one of my favourite features of Taronga's complex is the large fig tree in the third exhibit on the Tiger Trek loop (known, naturally, as the fig tree exhibit). It is quite an amazing sight to see a tiger climbing around the branches with ease. This exhibit also has a small pool, which I've seen tigers utilise on a hot day.
I'd also give a dark horse vote to the National Zoo and Aquarium. It's not the best exhibit, but has the capacity for 6 tigers I believe across four exhibits, and they are mostly quite large with lots of viewing opportunities. If all the tigers held were Sumatrans, I think that it would rank higher, although 4 of the 6 are generic hybrids.