I can only give you my experience as a PADI Instructor and I got mine when I was 50. PADI as I’m sure you know, is the most recognized organization internationally. That’s one reason why I went PADI. I would have considered NAUI but it’s not convenient here so I didn’t consider it as an option. Both organizations have a high emphasis on safety and education. When I go to the Caribbean, its PADI shops I see the most of. I’m happy with my choice and have my OWSI and my MSDT now. I would recommend that you talk to the course directors of both places where you’re thinking about taking your IDC and see if you have a good feeling after you leave. Trust your gut feeling and I’m sure you’ll end up making the right choice. If you have any specific questions, feel free to contact me.