I have to agree that as a non-average zoo visitor i find it hard to find much wrong with Edinburgh, as ive said in other threads i rate it probably number 1, since there's so much there that i can't regularly see at my local 'big' zoos,Having been there last week I can see how someone could come to that conclusion. Discussing the Zoo with a fellow traveller at the B & B* I stayed in, she said she'd took her nephews there and Blair Drummond and she thought the latter was better, "because it had all the big animals".
Personally, I disagree with the opinion (but I'm not the average zoo visitor) Edinburgh's a fantastic mix of interesting and obscure species pretty much all adequately housed (admitedly not in the prettiest enclosures sometimes) -my only grumble would be the lack of any significant number of Reptiles or Amphibians.
*Arden Country House, Linlithgow, guest house perfection, well worth the few extra pounds if you can afford them
Whipsnade, colchester or london.