You pose a most difficult question. They’re both great routes, just different. Pros and cons to each. Having just walked to Portugués Por La Costa just a few months ago, I can tell you it was quite enjoyable although we didn’t cut in until Vigo. We found the walking easier along the Costa route, but the Central, albeit cobblestoned most of the way through Portugal, had more of the Camino feel that we were used to. But, more road walking! Tradeoffs! We actually enjoyed the coast more above Caminha. Still, nice towns to stop in regardless of route.
So, if I were to walk in Portugal a third time, which route would I take? Probably the Central with the addition of the Variante Espiritual in the later half of the walk. To avoid the industrial section of Porto, walk out of the city along the Douro River to the coast and than north. As I remember, it was primarily road walking from Vila do Conde to Barcelos, but still good walking. A highlight of our camino was a night at Casa Fernanda. Quite special! Ponte de Lima, Valenca, and Tui great towns along the route. If I were going to take a day off, it would be in Pontevedra. So much history there! After that, particularly if you have an extra day, take the Variante Espiritual. There’s a very solid uphill which is challenging, but very doable. Most of it is on the road. The Monestario at Armenteira is another special spot. We enjoyed spending a night there. But, by far, the hightlight of the VE was the boat trip from Vilanova de Arousa to just outside Padrón.
Regardless, of the route you choose, I’m confident that you’ll enjoy your Camino.