Having made the move out of London 2 years ago I would say it also really depends where you are in life. Do you have children? If so how old are they?
If you have young children or you are planning to have them the success of your move will really be helped by being part of a primary school community, it makes a massive difference.
We moved with secondary aged children, we did look at Hitchin/letchworth (couldn't help but compare with London and it seemed second best) but ended up further out in a village (heart ruled head over a house) and I really miss being part of the community in the way I was in London.
If my children were smaller I'm sure I would be happier as I would have better links, but as it is we have struggled to find like minded people and our social life is still in London.
I love my house but feel I have lost out in too many ways and no house is worth it, but it's hard as we don't really want to leave the house, but living in a small village just makes me feels like I'm dead at times, mind you I think we are also in the wrong village.
We now have the dilemma of do we stay or go back to London knowing we can no longer afford to live where we did (very desirable part of N London) and like you have no desire to live somewhere on the way up having done that so often in the past (we lived in London for 27 years).
Hitchin is nice and has a slight edge to it, it's not all posh and fake, very easy to get to London and lovely countryside around, you can get a decent cup of coffee, meal out and haircut and the market is interesting. I don't know anything about the primary schools but think they are generally ok.
The problem re affordability in London is it's almost always impossible to bridge the gap when you want to move up. We did try and move to something bigger when we were in London but the gap was always too big and I don't think that will ever change, so you have to have a massive pay increase or have a large injection of cash from somewhere to allow you to move up the ladder, that was part of our decision to move out of London, that wish to have something bigger, but I now think it was slightly misguided.