Devizes is significantly further from the M4 though. I can be on the M4 in five minutes. From Devizes you'd be closer to 35/40 minutes depending on where in Devizes you are.
We didn't choose Chippenham, we sort of migrated here from Bath via Corsham. But it's become our home and we wouldn't move now (unless I could convince my husband to move to Cornwall). Our children are at an excellent Primary (Good Ofsted, but there's more to schools than an Ofsted rating) and Sheldon and Hardenhuish are both highly regarded Secondaries.
Easy links to Swindon, Bristol and Bath for shopping/days out. Trains run in both directions regularly or you can access them all in 25 minutes in the car.
Plenty locally too. Lacock is five minutes in the car, and we regularly cycle there and back too. Woods, rivers, cycle paths, skate park, toy library, dance school, gymnastics, leisure centre, gorgeous parks (one has a bandstand with a live band on a Sunday, people take picnics and the children play, it's a lovely way to spend a Sunday).
Town centre is not as grim as pp make out. Yes it has its fair share of charity and coffee shops, but day to day it's got what you need. There is a decent choice of supermarkets (only missing an Asda, we have the rest).
Good sense of community, events on at the Neeld Hall and the Cause.
Lots of lovely countryside on your doorstep for exploring (including Devizes and BOA). Without being too far from a train station or motorway, which is important for a city girl like me.
Downsides. Yeah, there are some not so nice areas, but I grew up in London and DH grew up in a Midlands city. The crappest areas in Chippenham would be seen as nice in those places!
Not much in the way of nightlife, but if you've got two young DC, then you're not going to be looking for that anyway. We tend to go to Rivo if we stay in Chippenham, or if we've gone to the effort of getting a babysitter, we go to a show at the Hippodrome, or for a few drinks on the Harbourside in Bristol.