I'm not sure it matters either way. Holy Week and Easter are particularly busy on the routes with Spanish pilgrims walking. The towns and villages are also busy where they have Holy Week processions...in the towns there are more hostals and hotels in the villages less crowds to take part in the celebrations. Let's see what others say but unless you want to see the holy week processions in a large town I'd plump for rural walking during this time.
I got caught without a place to sleep in Merida on the VDLP on the Saturday night of Easter in 2006.
I spent 2 hours walking and stopping to ask for a room in every hostel and hotel I came across. I also looked into the hotels listed in my guidebook. No luck.
My solution was to taxi 17 kms up the Camino to Alucen, a small village with an albergue that was not full.
I also learned that you can ask in a bar if they know of anywhere to sleep. They sometimes have rooms upstairs.