If it was me I would probably do Whipsnade if weather is good. Lots to walk around to see. Fanatastic seal lion show etc. with a bit to drive around too. I think you can get closer to more of hte animals by walking than you can by driving round Woburn IYSWIM.
OTOH if the weather isn't as good I would probably do Woburn as I think there is more indoors/in car. I havn't been there since I was a child myself though.
Never been to London Zoo - so can't comment on that.
Whatever you do look for some offers as you can cut the prices dramatically. I have seen free child entry to Woburn on the web somewhere. I think Toys r us Gold card gives 20-25% discount at London Zoo and Wipsnade.
Whipsnade is great, me and DH used to go even before DS came along. Don't go to London Zoo, it's depressing (small cages) and all the big animals have already been shipped out to Whipsnade. Haven't been to Woburn.
I love Whipsnade! Can't comment on other two, but personally think Whipsnade a fantastic day out for all the family. We've been there pre kids, and last year took the kids (then 3 and 6) - certainly plan to go again in another few years.
I really like Woburn and Whipsnade. Whipsnade is great for warm sunny days when you can stroll about the place. There is a lot of walking though as the animals have such lovely large enclosures in general.
Woburn is brilliant in that you can walk amongst the lemurs and spider monkeys and feed the parakeets (watch out for the poo though!!) Also on the safari bit the monkeys aren't nearly as destructive as the Longleat monkeys (shudders at memory of targeted destruction of car) One problem with the safari is that you would have thought it would be good for a rainy day, only with not being able to open the windows you can't actually see very much if its chucking down.
London zoo isn't great, its been years since I went and it was a foggy late November day - i think it had a reasonable variety of primates but can't really remember.
My aunt took my cousin (10yrs) to london zoo about a month ago, and they left beds by train about 9am and where back home by 2pm. They were very disapointed as animals were in concrete enclosures.
Whipsnade Zoo have very large enclosures. They have a new lemar enclosure where you can go in with them, a new lion enclosure and a new elephant enclosure and show. Can be Very windy as it quite open. (Food not over prices and good value/quality).
We always use the external car park rather than faff with driving round, there aren't that many places to park inside anyway, I don't think, so you'd still have to do quite a bit of walking. Also we have never bothered driving round the 'safari' bit, we just get the little train which goes past the elephants and rhinos etc.
We did last time we went, but i have to say this was because i was 7 month pg, dd is only 3 and itis quite along walk around the zoo. But more because we went with my dad who is terminal ill with asbestoes so can not walk far.
I don't know about tesco vouchers does it say amything on their web site. I do know if your prebook on the website you can save 10% of the enterance fee.