I hesitate to give you an answer because once your boots are on the ground & moving your perspective changes. I would recommend you read as much history of the Templars, the Cathedrals in Pamplona, Burgose, Leon, & Santiago. Along with the city defenses of these places. There is so much history recorded of this Camino (road) Even the ruins of the Hopitals along with the knowledge you are walking where old souls traveled simply will change how you move along.
I will simply stop now, as many others will give you an answer
Be sure to stop for a while east of Astorga at the special place known as the Casa de los Dioses on the alternative path after Villares de Orbigo but before Santibañez de Valdeiglesias just before the Cross of Santo Toribio. It is run by David Vidal who takes GREAT care to help passing pilgrims.
You can rest in the huge barn or simply enjoy his wonderful donativo goody shelf; I always stop. Once during a heavy rain although David was absent the thermos of coffee was hot and his cookies most delicious! His multilingual note read 'Welcome!'. After sitting sheltered, having a coffee and eating a cookie or two I left a donation and a brief note of thanks. Despite the cold rain this was a MOST welcome stop and a perfect example of yet another of the varied and generous caring alternatives available along the camino.... To each his own.
Villafranca del Bierzo. Nice town with interesting surroundings and with a good location for a rest day because next day you could go all the way up till O Cebreiro... perfectly rested.
Nothing wrong with Astorga either (as a town) but I think its location isn't so good for a rest day because it's at the end of the meseta and you would need to make the climbs to both Cruz de Ferro and O Cebreiro without a rest day in between. If you are going to take a rest day, I think it's better to make it somewhere between those climbs what would rule out Astorga (but take some time to visit Astorga even if you don't make a rest day there). If you plan to start in León, another downside to Astorga is that it's too close to León.
I'm facing the same dilemma and suspect I will let the weather and my body decide and probably go with the half day off approach.
Perhaps the lack of good suggestions means there's no place that stands out? Resting for a day in Astorga just two days after a rest day in Leon kinda misses the point. Viewed from a purely physical point of view, one can stop for a day anywhere just to gather one's resources either before or after the most strenuous days.
Me too! If in Villafranca del Bierzo you wish a bit of private comfort and/or a very good reasonably priced meal with delicious local wine do stop at the Hostal de la Puerta del Perdon. Located on the CF opposite the castle it is a very comfortable stop especially on a cold early winter night.
If the same people are in the albergue in Villafranca del Bierzo that were there in 2006, the hospitalero is a healer, people limp in and skip out, and there was a wonderful guy there who had just arrived and stayed on as a cook and assistant who showed us such kindness, in bitter weather in the middle of winter, and cooks up a storm for all and sundry each night. An absolute feel-good place.