Welcome to a life changing experience
Some hints and tips at choosing who you dive with:
First:
Learn in conditions similar to those you will be diving in. This is especially true for instructors. If you're going to be teaching in the cold, fresh waters quarries, an IDC in the bathtub waters of the tropics is going to leave you less prepared for your real world.
Second:
Your instructor is not supposed to be your friend. You want someone who will be tough, critical, focused and unforgiving. If you end up with a friend for an instructor (or someone who wants to be your friend) you can count on learning less due to the inevitable conflict between their dual roles.
Third
Talk to divers. If you're looking to become an instructor, talk to some instructors that you respect and find out who trained them. Check with as many dive shops as you can (especially the owners) and ask them who they respect and why. Local charter operations are also an excellent source of information on who the local instructors are that know their stuff.
Fourth
Talk to the instructor. Ask hard questions - how long have they been diving, how do they structure the class, how much teaching do they do, how much fun diving do they do, think of every "what if" you can and make sure you fully understand the answers and the program.
Fifth:
Ignore price. Unless you're just badge collecting, price is the least important factor. Quality, quantity, location, schedule, networking/placement services, etc., all count for more than price.