First of all, let me reiterate what Groundloop said about the management at Jerez. Also the staff are the same so there will be no difference in the standard and quality of training there.
Second, as far as potential employers preferring certain schools is concerned, apart from the reputation that some of them will have built up over the years, another possible reason is that the preferred schools tend to conduct integrated training as well. Now I know that the question originally was about modular training, but employers are better able to get the complete training record of potential employees from such schools if they have done integrated training, and perhaps the habit rubs off onto modular training. Just a thought.
Bottom line, however, is that the IR Skill Tset is the same for everybody, as are the written exams, so the end product ought to be exactly the same. Of more interest to the employer should be the applicant's success rate at passing the written and flying tests. To me, first time passes on a modular course should count for more than someone on an integrated course who took several goes to get through everything.