I think you need some idea of where you'll be working to narrow down the area! The valleys can be cheap, and you'll get more for your money, but commuting can be awful, especially along the M4. It takes DH 50 mins to go less than 10 miles.
Definitely avoid Newport though - you can't avoid the nicer areas for the type of house you want.
Rogerstone/Risca area was mentioned - very pretty area, but if you have Comp age kids, I'd be avoiding unless you can get a Rogerstone house in Bassaleg catchment.
The school catchments make a huge difference to house prices here, you'll get much more for your money in Risca, like this:
www.rightmove.co.uk/property-for-sale/property-83701697.html
which looks fab, until you realise its in High Trees, which is off Holly Road in TySign - an area so rough Royal Mail won't deliver to it! Plus its in Risca Comp's catchment area, so avoid!!!!
This house though, is in Rhiwderin, which is a popluar area, and Bassaleg catchment, much less for your money, but everyone I know would pick this over the Risca house!
www.rightmove.co.uk/property-for-sale/property-72021307.html