We are not going to argue what the best dive organization is, because it simply depends on your needs and wishes. If you want to work as a divemaster or dive instructor, think about what kind of job you want. Is it something you want to do between studies and work - as a gap year or do you see yourself working as a dive professional until retirement? Are you thinking of traveling around and working in different countries? Than you should select a dive organization that is (well) presented in those countries.
Of course, selecting a dive organization with a lot of dive centers give a lot more opportunities for jobs. Would you love to work in tourism / leisure diving in a tropical destination - than you should choose an organization where getting certified does not take 'forever'. If getting certified for SCUBA diving takes weeks of training, it is probably not what people will do during their holiday... Think about those things, ask yourself questions and do your research!