Hi - Hopefully Peter R will join in on this one too.
The route from A Coruna (as I understand it) is the more authentic route as records show medieval pilgrims from England (and Ireland?) arrived there more than any other place on the coast. I'm not sure any are recorded as arriving elsewhere. Nowadays there is a sailing ship from Ireland retracing the sea route and disembarking at A Coruna.
http://www.jeaniejohnston.ie/A Coruna is an interesting place - and some of the hotels on the front - with a very long promenade of 9kms - have wonderful sea views. One can sit and watch the early morning sea anglers on the beach and the afternoon surfers falling off their boards as really quite impressive surf gets up. There are historic sites like the Tower of Hercules.
However, as had been said, the distance to Santiago going straight to Bruma and then on down to Santiago is not enough to earn a Compostela. And truth be told, the walk out of A Coruna is rather tedious and it is understandable that some advise taking the bus for the first 7 or 10 k. After that however the route is interesting but in my opinion not bursting in character.
The route from Ferrol though less authentic in historical terms perhaps is a good walk with excellent views in places and stops in picturesque Pontedueme and Betanzos. It does qualify for a Compostela. For that reason it seems to have become the choice for modern pilgrims.
I found the locals on the Ferrol route much more aware of the Camino than on the A Coruna arm - but of course both are routes less travelled in comparison to others.
I hope this helps.
John