Having recently completed the Central Route from Lisbon, I would always defer to finishing in Santiago, but I also walk as a pilgrim, not as a tourist walking on a pilgrimage route. How 'true' a pilgrim I am might be debateable, but that is another matter.
If I weren't walking as a pilgrim, and was just interested in walking a scenic route through Portugal or Spain, I don't think it would matter much. More, I think it would be possible to find more scenic routes elsewhere than the Camino de Compostela routes, which are to some extent focussed on helping a large number of pilgrims travel safely on foot or by bicycle in as short a distance as is practicable for getting to Santiago.
My experience on the Central Route from Porto is that much of the first day is through urban areas. This may not have the aesthetic appeal you are looking for, but as a pilgrim it offers an insight into the places where a great many Portuguese live and work, and I didn't want to miss that. I am told that the Coastal and Littoral routes offer more attractive scenery on that first day in particular.
And I found there were plenty of private accommodation places supporting both stretches of the routes you are contemplating. While I did stay at some pilgrim albergues when they were available, my view is that one could craft a tourist itinerary around private accommodation if you were walking this route as a tourist.
