You'll have to do your own options analysis for Paris vs Barcelona. I'd consider factors such as cost, schedule, and how to get home from Santiago.
Barcelona
City of Barcelona
http://www.bcn.cat/castella/laciutat/
Area Metropolitana de Barcelona
http://www.amb.cat/s/home.html
Airport
Barcelona Airport (BCN)
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-Barcelona/en/Home.html
Connect from Barcelona Airport to Train and Bus Station - Sants - with Renfe Cercanias/Rodalies R2 from Terminal 2. The train runs every 30 minutes. Time to Barcelona Sants is 22 minutes.
Connect from Barcelona Airport to Bus Station -Nord - with Renfe Cercanias/Rodalies R2 from Terminal 2. Transfer at Sants to train R3 or R4 to Arc de Triomf stop then walk 300 meters along Av de Vilanova to the station.
Alternatively, connect from Barcelona Airport to Bus station -Nord- with Aeroport bus from either T1 or T2 to Placa Catalunya. Walk from Placa Catalunya via Arc de Triomf to the bus station, a twenty-minute walk (1400 meters) or take the Metro L1.
There is a shuttle connecting Terminal 1 to Terminal 2.
There are several bus companies providing service from Barcelona Airport. See the Airport website transport and access.
Getting around in Barcelona
Shuttle Bus from Airport to Barcelona Center
http://www.aerobusbcn.com/
Transportes Metropolitans de Barcelona
http://www.tmb.cat/es/home
Autobuses Metropolitanos
http://www.amb.cat/s/home.html
Renfe Cercanias/Rodalies Barcelona Light Rail
http://www.renfe.com/EN/viajeros/cercanias/barcelona/index.html
Ferrocarril GenCat Light Rail
http://www.fgc.net/esp/index.asp
Trains
Barcelona is connected by Renfe to destinations such as Pamplona, Santiago, and Madrid.
Barcelona is connected by Renfe to border crossings at Irun/Hendaye and Port Bou/Cerbère where there is break of gauge connections to the SNCF rail system in France.
Renfe and SNCF have recently started rail service direct from Barcelona to Paris.
Barcelona Sants (Renfe Station and Estacion de Autobuses)
http://www.adif.es/es_ES/infraestructuras/estaciones/71801/informacion_000097.shtml
Renfe
http://www.renfe.com/EN/viajeros/index.html
SNCF
http://www.sncf.com/en/passengers
Buses
Several bus companies depart direct from the airport
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-Barcelona/en/Home.html
Barcelona Sants (Renfe Station and Estacion de Autobuse)
http://www.adif.es/es_ES/infraestructuras/estaciones/71801/informacion_000097.shtml
Barcelona Nord Estacion de Autobuses is the main bus station in Barcelona
https://www.barcelonanord.cat/inici/
Ships
Port of Barcelona
http://www.portdebarcelona.cat/?WCM_GLOBAL_CONTEXT=/wps/wcm/connect/ExtranetCastellaLib/El%2520Port%2520de%2520Barcelona/El%2520Port/Portada
2350 Barcelona to Saint Jean Pied de Port
2351 This section describes transportation options from Barcelona to SJPdP.
Option 2352 and 2353 take about the same travel time either way ... so its dependent on your travel plans which is better
Option 2355 is the easiest way to get from Barcelona to SJPdP. However, bus service from Pamplona to SJPdP is seasonal and limited in number of departures.
Index 2350
2352 Barcelona to SJPdP via Toulouse by Train
2353 Barcelona to SJPdP via Irun by Train
2354 Barcelona to SJPdP via San Sebastian Airport and Bayonne
2355 Barcelona to SJPdP via Pamplona by Train and Bus
2352
Barcelona to SJPdP via Toulouse by Train
SNCF and Renfe operate trains from Barcelona (Sants) to Toulouse (Matabiau). Use SNCF site.
There is a high speed train to Paris that stops in Toulouse. Other trains transfer at break of gauge station Port Bou/Cerbère and require transfer at Perpignan or Narbonne before getting to Toulouse.
SNCF operates trains from Toulouse to Bayonne.
The final leg involves SNCF TER train #62 from Bayonne to SJPdP.
SNCF
http://www.sncf.com/en/passengers
2353
Barcelona to SJPdP via Irun by Train
Renfe operates trains from Barcelona (Sants) to break of gauge stations at Irun/Hendaye.
Irun Renfe Station and Gare d'Hendaye are train stations 3 km apart.
Note that an end run might be possible by traveling from Barcelona to Miranda del Ebro (where trains from all over Spain converge) and then to Irun.
Euskotren operates a commuter train from Irun Colon Station to Hendaia Station if needed.
Euskotren Colon Station: exit Renfe Station, turn right, walk across bridge over the tracks and find Colon Station on the left (North) side of the street. Hendaia Station is co-located with Gare d'Hendaye.
SNCF operates TGV and Intercites trains from Irun and TER trains from Hendaye to Bayonne.
The final leg involves SNCF TER train #62 from Bayonne to SJPdP.
Renfe
http://www.renfe.com/EN/viajeros/index.html
SNCF
http://www.sncf.com/en/passengers
Euskotren
http://www.euskotren.es/
2354
Barcelona to SJPdP via San Sebastian Airport and Bayonne
Fly from Barcelona Airport to San Sebastian Airport. The airport is almost co-located with Irun train station.
Take local bus or taxi to Irun Renfe station or Gare d'Hendaye.
SNCF operates TGV, Intercites, and TER trains from Hendaye to Bayonne.
The final leg involves SNCF TER train #62 from Bayonne to SJPdP.
Barcelona Airport (BCN)
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-Barcelona/en/Home.html
San Sebastian Airport (EAS)
http://www.aena-aeropuertos.es/csee/Satellite/Aeropuerto-San-Sebastian/en/
SNCF
http://www.sncf.com/en/passengers
2355
Barcelona to SJPdP via Pamplona by Train and Bus
This option is the easiest way to get from Barcelona to SJPdP. However, bus service from Pamplona to SJPdP is seasonal only and limited in number of departures.
Travel from Barcelona to Pamplona by Renfe train or by bus. Trains leave from Barcelona Sants. Buses leave from Estacion de Autobuses Barcelona Nord and Barcelona Sants. ALSA (with transfer at Zaragosa) and ViBASA are major service providers on this route.
There is seasonal bus service from Pamplona bus station to SJPdP provided by Conda. Conda is owned by ALSA. See international schedule on ALSA website. Purchase ticket at Pamplona bus station.
At time of writing bus schedule from Pamplona to SJPdP: 1000 13 June to 31 August 2014, 1430 1 June to 30 September 2014, and 1730 17 March to 30 September 2014. Schedules are usually updated only 30 days in advance.
Renfe
http://www.renfe.com/EN/viajeros/index.html
ViBASA (Monbus website)
http://www.monbus.es/es
ALSA
http://www.alsa.es/en/
Conda
http://www.conda.es/