I have numerous Catalan friends with differing views on this subject. One is a freelance writer, who advised me to study Castellano (Spanish) because if you want to travel to other parts of Spain, or other Spanish speaking countries, they wont understand Catalan.

Another is a deputy head master at a school here, he strongly advises that if you have children in school, then you should learn Catalan so that you can converse with your child as he is learing the language, and support him with his studies as well.

Personally, i stayed with Spanish, although i can understand a lot of Catalan, but cant really speak it. Also depending on if you are planning to work here, we have a lot of Spanish speaking clients, so for me, Spanish is essential, Catalan is not, and i just dont have the time to study both languages, or have the space in my head either........lol

My Son's teacher's, and parent's of other kids, speak to me in Spanish, although all correspondance from school ie: letters, school reports are in Catalan.

It is much easier to find teaching aids in Spanish, books, CD's etc, but many of the local Ajuntament's (town halls) offer free Catalan classes to foreigners, but these didn't coincide with my own time table.

So i suppose the answer is, whatever is best for your own circumstances and life style, and how much time you can dedicate to either. One language is hard enough to learn for adults with busy lives, two is a mammouth under taking!

Hope this helps.