I agree with falcon on this one. I have walked all of these routes into Santiago and was just back on the Francés this past July. I marveled many times at how I had forgotten how beautiful the scenery was. I joined the Francés in Ponferrada and enjoyed every step.
Though I love the Primitivo-Salvador combination, in fact it´s probably my all time favorite, the part from Lugo isn´t really that beautiful in terms of scenery. At least in my opinion. It is not that hard to avoid the Francés rush when you join from the Primitivo, though. If you spend your last night on the Primitivo in Ponte Ferreira, then walk the next day through Melide and on to Boente, you can avoid some of the craziness, because Boente doesn´t have beds for many more than 50 or 60 pilgrims. I even found I could avoid the last day´s madness by continuing on past Arca do Pino and sleeping outside Lavacolla in the beautiful little place Casa de Amancio.
All in all, I would say that the last 100 km are not the scenic high points of any Camino, but they are all enjoyable. The Portugués might also be worth a look. Buen camino, Laurie