One day trip in wales

Looking at doing into a trip into wales from the oxford area tomorrow. Probaly going to head down to cardiff in the morning then not sure where to go, are there good roads along the coast or is it best to head for central wales?

Cheers

if you can stay away from the coastal town and traffic all the other roads are great! my faves are the Brecon beacons national park, llandovery, lampeter, tregaron (the pass is loverly) and then up to devils bridge. watch out for plod tho.