In 2009 I walked Ferrol to SDC.
In 2010 I walked Sarria to SDC.
I have stents and two of my arteries are 90% narrowed. Throw in diabetes, some kidney failure, some loss of sensation in my feet and that's me.
Sarria is best. More people to help if you get into trouble. More bars to stop at. Albergues far more frequent. More roads, buses and taxis to call.
While the topography from Sarria is downhill, be aware that the Camino crosses a number of river beds so there is still plenty of hills to go up.
What is significant is that the hills on the Camino Ingles are higher and more strenuous. Indeed the climb out of Pontedeume is steep, long and challenging.
The blunt truth is if you need medical help or have to abandon your Camino it will be far easier on the Sarria to SDC route.
If you find that this route gives few problems then you might come back to the Ingles at a later date, but for now undertake the Frances.