I'm weighing in with a different perspective.
I recently took a couple of people to walk on the Sanabrés - one to whom the Camino was completely new, the other having walked parts of the CF before (but not the last bit).
We started walking the Sanabrés but it was lacking in infrastructure and interaction with others. So, after a couple of weeks and on my suggestion, we abandoned it and went to Sarria and they walked from there to SDC. I still want to walk the Sanabres in its entirely, but for them, the
Camino Frances was so much better. Pretty countryside, beautiful soft walking, lots of places to stop, they met and bonded with other pilgrims, got to Santiago, got their Compostela, and it was everything we wanted it to be (putting aside the nasty fall on the last day....)
It is the total experience that counts. For that reason for first timers I suggest Sarria to SDC over the Sanabrés or other less known routes. I think sometimes we forget that people looking for the camino "experience" are not looking for a beautiful solitary walk. That can be done in many, many places in the world, and probably better. They are looking for something unique, and to me, that means the Camino Francés. The daddy of them all.
Lots of old timers here will steer you away from the last 100km, because they perceive Sarria to SDC on the Camino Francés as too crowded, too popular, too whatever, and they compare it unfavourably to quieter sections. My view is that if you have not walked a Camino before, then you have no comparison and it will not disappoint you.
I've never come across someone who walked their first camino from Sarria, and subsequently wished they'd walked a different camino instead.
If you do have time, then my suggestion is to start from further back. Longer is always better! If your time is limited then do not waste it on buses skipping sections - start somewhere and keep walking until it is time to go home.
Whatever you decide - I hope you have a Buen Camino!