I will be starting my first Camino from Roncesvalles in late April. After reading several entries on this forum and looking into the bus and train schedules, I discovered what I think is the easiest or at least a simple way to get there.
I am flying from Canada to Madrid and then on to Pamplona - all in the same day, and on the same plane ticket. Arriving late, I will spend the night in Pamplona and then catch the 6pm bus the next day to Roncesvalles. This gives me the day in Pamplona that I can use to mail stuff forward to Santiago so that I do not have to carry it from Roncesvalles and also to explore the sights.
When you buy your plane ticket ask for prices that include the extra 1 hr hop from either Madrid or Barcelona to Pamplona. Then compare that to the bus fare from each city and the cost of accomodation/transportation if you have to spend an extra night in either Madrid or Barcelona, depending on when your flight arrives from home and when the bus to Pamplona departs.
Good luck!
Marilyn