My opinion would be that your limitations will be budget, size and availability...
We quite like living within zone 10 of zurich...there's no reason why you *need* to go as far as Horgen or Thalwil...really depends also exactly where the job is...
My experience so far is that there are expats all over the city - if you did a survey of the people here on the forum I get the feeling you'd get a sense of them being mostly in the Thalwil/Horgen/Oerlikon/Alsetten areas - but this is probably more because that is where there is lot of housing...
With the consideration of having a small baby, my advice would be to consider whether you want to live with or without a car...
Essentially, you can't drive around central Zurich, and parking in the city is a nightmare, so if you live, work and travel in the city centre, consider relying on trams, buses and the occasional train - about half the trams and buses have low floors which make it easy to get a pram on/off - and I have to say in 9 months of pushing a pram on and off the trams (no car)...someone has offered help *every time*!
Another expat with a small baby is living in a house down the lake and she said getting on/off the trains with a stroller is a *nightmare* - partly because the commuter trains have two enormous steps to get on and off, the trains don't necessarily wait for you (they might not notice if you have a problem), and often you are getting on/off and other people are not there to help - at least with the trams/buses there is usually at least a dozen people around to help if needed....
Have you lived in an apartment before ?
Living in one with children can be quite a challenge...BUT we find it a lot more 'efficient' in terms of cleaning, heating, and cost - and as a mum who is home a lot, I feel safer in an apartment block where I know there is the old lady downstairs if I have any major emergencies (like when I misplaced my keys and she let me in out of the snow!)...it can feel very isolating at home on your own, especially in a foreign country...
Sorry to rave on...feel free to PM me if you want any more 'baby tips' and you'll find quite a few other expat mums around too!