SSI-PADI-SDI-NAUI-YMCA-TDI
Looks like the alphabet soup of SCUBA diving. By the way, SCUBA stands for “Self Contained Underwater Breathing Apparatus”.
The well-known, internationally accepted scuba certification agencies:
SSI = Scuba Schools International
PADI = Professional Association of Dive Instructors
SDI = Scuba Diving International
NAUI = National Association of Underwater Instructors
YMCA = Young Men's Christian Association
Schools will feature one of the above because they like their training materials, and teaching philosophy. Many programs only offer recreational scuba training through organizations belonging to and adhering to the teaching standards of the RSTC.
The Recreational Scuba Training Council (RSTC) was incorporated in the United States in 1986. RSTC’s mission is to establish minimum training standards at all levels of recreational scuba diving in order to promote public safety. The RSTC is also the Secretariat for ANSI Committee. (American National Standards Institute).
Of the above list of agencies, only NAUI is not a member of RSTC. NAUI is a fine organization and one of the pioneers of SCUBA certification. I would not hesitate to recommend NAUI to a friend if I knew the instructor.
The main mission of certification agencies is the Marketing of Scuba Diving. Some do a better job than others. The organizations you have heard of have done a better job of selling their brand.
The dive course you take is going to be no better than the instructor who teaches it. So how do you choose?
Go to a reputable Dive Shop or University. Meet the people who represent the shop or school. How long has the scuba instructional program been in existence? Does the store or school monitor their instructors? It is possible to get a great course from an independent instructor but I don’t recommend it unless he or she is recommended by a close personal friend that was certified by that independent instructor.
The Good News:
Finding an experienced, highly qualified instructor is not that hard.
The Bad News:
The course will probably be a little more expensive. Good people don’t have to work cheap.
The sweetness of cheapness is not long remembered.
Have fun. Go diving
Barebones