You get to decide just after Villaviciosa. About 3-4km after the town, you reach a village called Casquita, where there are arrows pointing to either Oviedo or Gijon. It's quite a walk to both places from Villaviciosa: Gijon is 29km, and Oviedo is 44km (so normally walked in two stages). It's only the last few kms into Gijon that are a bit industrial (it's a city, after all), and because the stage is so long, lots of pilgrims choose to catch a bus from the city outskirts. Personally, I quite like the city sections, as it reminds one of "the good, the bad, and the ugly", all part of life.
If you choose to go to Oviedo, there are a few albergues along the way that allow you to break the stage up. Some info
here. Oviedo is a great city, with a famous cathedral (home to the "sudarium" or cloth used to mop Jesus' brow during the crucifixion).
[Edit: disclaimer!! the description below, which comes from Gronze, appears to be inaccurate. In the post below this, Laurie provides an alternative description of the Villiviciosa-Oviedo-Aviles variant]
But the walk into Oviedo is also very industrial. According to Gronze: "Entry to the city of Oviedo consists of 5 kilometers of highways and industrial estates, not exactly a dream landscape for the pilgrim." You'd then have to walk 29km from Oviedo back up to the coast at Aviles. You'd basically be walking through the outskirts of Asturias' 3 main cities, however, so it kind of defeats the purpose of avoiding the industrial zones! To translate what Gronze says: "This linking stage to continue the Norte along the coast sees few pilgrims... A significant part of the stage goes mostly through urban, commercial and industrial environments, although there are a few pleasant rural and wooded sections."