>>17859857 (OP)Depend which ancient times you meant
During the Bronze Age most of Spain was a celtic shithole, but there was Tartessos being a somehwat large civilized organized kingdom. Meanwhile, Gauls were unilaterally tribal, mostly unorganized societies.
After the end of the Bronze Age, the collapse of international trade and Tartessos quite literally sinking in silt, Spain had little to zero civilized areas. Most were Phoenician enclaves. Gaul was much the same at the time, with Massalia serving as the singular center of civilization unequaled by any kind of celtic settlement until the constructions of the oppidae from around 200 to 50 BC. Basically I'd say they were even because Massalia was fucking massive compared to places like Gadir, because it was a neuralgic center on the Tin Road.
Carthage conquered Iberia but didn't do much with it except conscript auxiliaries and mercs into the Barcid private army.
Then Rome forcibly made the question moot with both when they conquered them. The eastern coast of Spain and Southern Coast of gaul became highly urbanized, being around the main trade area of the Mediterranean, while the rest slowly urbanized
tl;dr Spain was maybe a bit higher than Gaul during the Bronze age but kind of regressed and then both were mostly equal in economical and development stature until the end of Antiquity.