Moderator, Iberia Airlines, Airport Lounges, and Ambassador, British Airways Executive Club
Join Date: Feb 2010
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Posts: 63,791
It depends on your frequent flyer scheme, but essentially Iberia's scheme gives you credits and lounge access (etc) if booked with an IB code, anyone else does not get these benefits. Vueling isn't a oneworld airline.
For seat selection you best use Vueling's own app at OLCI, it's usually easy enough to get a preferred seat then, and to change it if necessary. If your e-ticket gives you one checked bag, then that is what you will get unless you are on the Iberia frequent flyer scheme.