Where in Tennessee are you located? There may be more than those two to choose from. I am also going to suggest that you read this :
http://www.scubaboard.com/forums/new-divers-and-those-considering-diving/283566-responsible.html
and this:
http://www.scubaboard.com/forums/ne...ring-diving/287780-excellent-scuba-class.html
Once you have done that I might also suggest a copy of this :
SCUBA: A Practical Guide for the New Diver: James A Lapenta: 9781494900250: Amazon.com: Books
All of these were written with you in mind. You will get a lot of opinions that all basic OW classes are the pretty much the same. This is not true by any stretch of the imagination. The standards that you are to be taught to are different, have different skills, different minimum class times, different minimum content, and can vary greatly based on the person teaching it even in the same agency guidelines.
The first thing you need to ask yourself is "What am I really doing getting certified to scuba dive?" Here's my opinion - Getting a certification to scuba dive is embarking on an adventure. One that takes place in an environment that is normally hostile to human life. We do not have gills. You need to use a mechanical device (with multiple ways of it being able to fail) that requires specialized training to use safely and maintain to exist in that environment. You are entering an environment, and frankly a way of life, that is exciting, educational, relaxing, fun, and offers the opportunity to experience what 95% of the rest of the population will never experience.
At the same time it presents an element of danger and risk that can be reduced, but never eliminated, by good training, experience, and following safe diving protocols. The element of danger that is manifested under water is often found by going too far, too fast, outside of your training and experience, and by accepting less than comprehensive training in scuba. Those items can result in serious injury or death in some very nasty and creative ways.
So what do you think would be the type of training to seek out? Quick, very basic info, and with the risks glossed over to minimize the time required? Or comprehensive training based on skills and education that may take a little longer but greatly increase your independence and ability to dive safely and be a good dive partner?
The fact is that it is possible to get the latter in any agency. But you can only do that by finding the instructor willing AND able to take the time necessary to impart that information. How you find that instructor is by treating them like any employee you would be hiring. That is what you are doing. Hiring an employee to work FOR you to teach you the necessary skills and pass on the necessary information to not only survive but have a boat load of fun.
So you need to interview that person. Think of the kind of interview you would conduct on someone who was going to care for your children and go by that. The kind of questions and background information you'd want. References. The one thread I noted has a number of questions to ask. The book I linked to has even more and other information that I think every new diver should have.
What are they teaching you? What should they be teaching you? Ask them to see in writing what they should be doing. Every agency has written standards they must follow and content they must cover. It's all spelled out in plain English. Ask them to see those standards and ask them how they compare to those of other agencies. They should be able to tell you. Some may not since they have not taken the initiative to find out. I have the standards for nine agencies in my personal library. I'll show any student all of them.
Many people put more thought into buying and selecting a new TV or washer/dryer than they do selecting a scuba class. This can come back to bite them big time.
So, PADI or NAUI? Neither. Until you have done your homework and discovered the best avenue of training for you after checking as many as you can. Don't forget about SEI, SDI, SSI, etc. Also look into classes at your local university and with independent instructors. There is a great program at Middle Tennessee State University run by a personal friend and dive buddy. She has been teaching there for a while and is someone I would send my kids to.
That's another thing to consider when selecting an instructor. Would I trust them to train my loved ones?