You won't go wrong if you choose either Oxford (OAT), Aviation Training Associates (ATA) or Bournemouth Commercial Flight Training (BCFT). The difference between them is not particularly one of training quality but more how you are treated as a student. ATA and BCFT tend to have slightly older students on second career paths, dress is casual, instructors wear civvies. OAT tend to have younger students and provide a more regimented course.