Have a look at Chingford, it's classed as london although its historically part of Essex. Epping Frorest is in your door step, family friendly and 20 mins from Liverpool street or a bus ride to Walthamstow which puts you on th Victoria line and in the west end in 20 mins.
this is what yiu would get within 5 miles of st albans http://www.rightmove.co.uk/property-for-sale/find.html?locationIdentifier=REGION%5E1244&maxPrice=300000&displayPropertyType=houses&oldDisplayPropertyType=houses&radius=5.0&includeSSTC=true&_includeSSTC=on&googleAnalyticsChannel=buying
Not especially familiar with the areas you mentioned. We looked at St Albans when we moved down to London a few years ago attracted like you by the fact that we'd be the right side of London to visit family. In the end though we ended up in South East London because although the journey north is longer, DHs commute was much better, and we figured that was 5 times a week versus much less frequently.
We live in Essex on the train line into Liverpool Street. It's handy for the City, Canary Wharf and the Stratford area. Train service is very good but property costs are high. Excellent schools and facilities.
As pootlebug says, it all comes down to the area you need to get to each day.
Whereabouts in London will you/your DH be working? Where to live outside is often determined a bit by that, and train lines....it's much easier and quicker to do overland train + short walk than overland train + 2 tubes, for example.
We are relocating to London with a 2yo and a 3mo. With a budget of about 300k, I don't think wecan afford to live in London itself, so we're looking at commuter towns. We're considering St Albans, Welwyn Garden City or Hemel - does anyone live there? Are there a lot of young families and is there much to do with preschoolers? What is there in the way of facilities - leisure centres, libraries, der/dentists?