How should I choose what I want to study?
The first thing you should do is find out the content and objectives of each course by reading the different syllabuses. For more information, read the following page:
http://www10.gencat.net/dursi/uk/sortides/index.htm

What is the difference between officially-recognised qualifications and UAB qualifications?
Officially-recognised qualifications (licenciaturas (degrees), diplomaturas (diplomas), ingenierías (engineering degrees) and ingenierías técnicas (technical engineering diploma) are recognised by the Spanish Ministry of Education and Science, and the courses enable students to obtain a degree that is officially valid in the whole of Spain. The UAB qualifications are only endorsed by the university itself, and their value is based mainly on their acceptance in the employment market.