Stortford actually has a train station, which SW doesn't!! Stortford feels better connected to London than SW to us - you can easily live here without a car, which I feel would be a struggle in SW.
I like that Stortford has pretty much all you need in a town - all the main banks, big central supermarket, small high street with the usual stores (Waterstones, ELC, M+S, WH Smith, Monsoon, etc), plus some nice places to eat, all of which seem pretty child friendly, dentists, doctors, hairdressers, shoe shops etc. But if we need something from a larger town, Harlow is nearby, as is Cambridge or London.
I only have 1 child under 3, but from what I can tell, schools here are great - our childminder has her children at one of the local primaries, and from what interaction I have with them and their friends, I would be really happy for DS to go there! We moved here from London (and a short stint in a College town in the US) and it feels like a separate town without feeling isolated from the real world - I have only visited SW, and driven through it on the few occasions the M11 is closed (as I work v. close to it), but it feels more olde worlde and not part of reality - in a good way, but we would find it frustrating.
DH commutes to Liv st though, and finds the train link mainly excellent. We used to live on the other side of London and he used Worst Great Western for a while, and says NEEA is a breeze in comparison, although full of (his words) 'bloody foreign tourists' (he is a foreigner, so I always find this description ridiculous!!). I commute to work via the M11, and although I hate motorway driving, it is pretty good - never massively busy.
If you are looking in this general area btw, Stansted Mountfitchett is nice, as is Sawbridgeworth :) and both are on the train line to Liv St.