First off, let me just say I'm Singaporean, and damn proud of our Zoo. And it is an award-winning zoo, so we have reasons to be proud of it.
But this is a comparison of two zoos, mainly because I have been to the Ueno Zoo recently (early Nov 2016), and returned to the Singapore Zoo recently (early Dec, 2016) and the impulse to compare and contrast was strong.
Anyway, these are just my impression, and, spoiler alert, I think the Singapore Zoo is much better generally, although there are some good points with Ueno Zoo.
Firstly, Ueno Zoo is much more affordable. At 600yen per adult admission, that works out the about S$8.
SG's Zoo admission for adults is $33. Four times that of Ueno. For just my wife and me, that would be S$66. Fortunately, my daughter is only 2, and she has free admission for Ueno and SG Zoos.
Food was also costly in SG Zoo. A plate of Chicken rice was $9.90. A Hotdog set was $7.90. It came with a small plate of fries. Drinks prices were ridiculous. Three ice lemon teas and a black coffee (Kopi-O) was almost $20. The ice lemon tea came in souvenir tumblers whether you wanted them or not. There did not seem to be any simple, low cost option. Later I saw a vending machine. All the drinks were priced at $3.50! It would be about $1.20 - $1.50 anywhere else.
We tried the fast food joint at Ueno. It was not cheap, but not remarkably expensive. It was perhaps at a slight premium. The fried chicken we ordered was, like all Japanese food, tasty. The fried chicken set with a drink, came up to a little over 1000 yen - or about $14 per meal. We were just peckish, and needed a rest, so we just shared a set. All of us had something to snack on.
And when I looked for vending machines, the prices were the same as anywhere else in Tokyo, or Japan for that matter.
So in terms of affordability, Ueno Zoo wins.
Another point in Ueno's favour, but not through any effort of the Zoo management, is the climate. We visited Ueno in November, which would make it mid to late autumn. Temperatures were about 12 C in the day. It was cool, even cold at times, and it was enjoyable (at least to this over-heated Singaporean) to walk in the cool autumn day. (Note: about 12 days after we left Tokyo, it snowed for the first time in over 50 years in November.)
While the zoo is quite large and sprawling, it was not overly large and was eminently walkable, and walking about was enjoyable in the cool autumn day.
We visited the SG Zoo in Dec. And there only 3 seasons in Singapore - the Hot Season, the Hot and Wet season, and the Hotter and Wetter season. Dec is either the Hot and Wet, or the Hotter and Wetter season. In any case, I perspired - no, sweated - a lot. The main Zoo (there are two other spin offs) is within a huge sprawling compound, and to save our legs from exhaustion, we got tram tickets which allow us to hop on and hop off the trams as needed. The Trams served 4 stops, around the zoo, and costs $5 per adult (again, my daughter rode free).
Ueno also had a monorail with just two stations. You could take it to save a bit of walking, but it isn't absolutely necessary. It was 150yen per ride, but you pay per ride. If there is a crowd or a queue, you may as well just walk. It would be faster.
So the three things that Ueno had an advantage were, admission was very affordable, the zoo was not too large - enough to spend a day exploring, but not so much that it would tire you out, and the climate was very agreeable. At least in November.
So for $8, you could spend most of the day in the zoo, and for another $14 you could have a pretty decent meal. And drinks won't bankrupt you.
The SG Zoo would also take up the whole day, but it would cost you $33 just for admission, $5 if you want a Tram ride now and then to take the load off your feet. And if you needed a decent meal, it could set you back more than $15. And with the heat, you will need a lot of water, and that could burn a hole in your wallet.
Okay, but what about the animals?
Ueno Zoo is... well... a zoo. There are cages, and bars, and pens and the animals were in them. Quite a few of the enclosures seemed rather small, but you could see that some effort had been made to "landscape" the enclosures so there is some semblance of the animal in its natural habitat.
Ok. That sounded a little... patronising.
I can't help myself.
It's not a bad zoo. I'm not an animal welfare activist so I'm not overly concerned about animals in captivity. I believe zoos have a purpose, but they also need to try to cover their expenses, so profitability and costs are considerations.
There are too many ways to compare the two zoos so I'll just pick one animal they both had in common - pandas.
The pandas in Ueno Zoo are in huge cages, with lots of greenery, and of course bamboo. Visitors stand outside the cages and gawk at the pandas. Pandas apparently have to be separated. So each have their own cage. And each panda is sitting or lounging against the greenery, eating bamboo. (Bamboo is not very nutritious, so they have to eat a lot of it all day long. Or most of the day. It's like if all you can eat is celery (which isn't very nutritious either, I hear), so you have to eat a ton of it (or about 20 kg of bamboo a day for the pandas.))
The cage is not obviously unpleasant. They are quite large. But the setting is obviously a zoo.
The pandas in SG are not in the main zoo, but in the "River Safari" - a river-themed zoo with separate admission). The pandas are in an air-conditioned exhibit which is landscaped with a small hill and greenery, and bamboo groves. And the pandas (also separated) lounged on the hills in their respective enclosures. Yes, there are walls and gates, but the visitors view the pandas from an elevated walkway, and have an unobstructed view of the panda - well, unobstructed by cages, wires or bars.
The feeling is almost intimate. Natural. Almost as if you came upon the pandas in the wild, while taking a walk through the cool forest. (But this is subjective, of course.)
And this effort to exhibit the animals in as close to their natural habitat as possible, or in an unobtrusive manner as possible is evident for quite a few other animals. One of the first exhibits as you enter the main zoo, is the tamarin exhibit, which looks like a thick grove of trees and underbrush right in your path, except for the 4 or more cotton-top tamarin. Uncaged. This is the start of the Tree-Top Trail, which brings you close up to the inhabitants of the forest tree tops.
The white-face Saki Monkeys are another "uncaged" exhibit. They were left to roam a small "forest" which you can walk right up to. One was draped over a service gate with it's tail temptingly drooping down within touching distance. We had to touch it to confirm it was not fake of course.
The Siamang (an ape, I think they are from the gibbon family) also appears to be uncaged, though they kept their distance, up in the trees.
Overall, the SG zoo showcase their animals better, and I think visitors get that.
But you pay for that quality.