well, more space is fine but it doesn't mean much unless...
a) you can get your hands on animals to fill that space, and we all know how hard it is to get an antelope around here!
b) you have the people to come visit.
i agree monarto has got a very bright future. i also think western plains is sadly a sinking ship. but if we mean "the one to watch" as in the zoo set to take the lead as australia's premier open range zoo - then i think the zoo poised to take that title is werribee.
compared to monarto, werribee still also have a large amount of undeveloped land at their disposal. also, i've only seen photos of the other two open range zoos, but werribee have some damn nice land at that. the way taronga beats melbourne on topography, i reckon werribee beats all other open range zoos. not that i have faith they'll do it - but that zoo could get a DAK worthy makeover.
but most importantly - werribee have three times the population of adelaide just 45mins away.
and a massive amount of animals at their disposal, like elephants. zoos SA currently have more stock at their open range zoo - but from what i gather its all low key cheaper developments, like at dubbo. werribee have far less animals, but the ones they do have are high profile and have big a-grade immersion style habitats - like the hippos. surely that exhibit is worth ten cyclone-fenced carnivore exhibits.
they have also made significant progress with immersion landscaping, and that counts for a lot. thats an aweful lot of work. the way i see it, werribee dont have much at present, but really strong foundations. their poised to kinda just smash it in the lead stakes because they have done much of the hard stuff already. in the next ten years i see elephants, gorillas (not that i'm happy about that) chimps and all the other little monkeys and stuff moving out there.
so, based on potential alone, and i'm not being biased, werribee is gotta take an unbeatable lead eventually. just based on location to melbourne alone....