I couldn’t tell you which is the best as I’ve only done training with PADI as they are the most accessible in my area. I felt my o/w training was adequate. I felt comfortable enough getting in the water.
I took some advanced training and specialty training through PADI instructors. I don’t know if it was the instructors themselves or the methodology behind it, but I did NOT feel advanced or specialized. I didn’t think the training was adequate.
I took a B1 course and am currently taking a B2 course with an instructor who is also a GUE instructor. PADI’s buoyancy course is what? some bookwork and an o/w dive? This instructor gives a 6 week course with both classroom and pool work. The course was/is really militant, but I learn a lot from him. Example, after I took his B1 course, I went on a dive trip with new friends (who are all instructors, work for a charter co. in Maui and dive 4x a day almost every day), and I had just over 50 dives at the time. Six months later, I email them saying I just made my 100th dive. They were like "no way, we thought you had at least 250 when you were diving with us".
Is GUE better, or is the instructor better? Well, it’s really a PADI course taught with GUE methods. The instructor turned a 2 day course into a 6 week course, with the option of an additional 6 weeks of training.
I won’t be getting any certification with the B2 course, but I’ll be a better diver, more comfortable in the water and will have more fun because of it. Is 12 weeks of training worth it? I think so. But we each make our own choices.