I am recently certified. I started with a local Dive Shop with the SSI program. I felt the classroom work was mundane but the pool work was intense. The instructors were good and cut no one any slack. Either you did it correctly or they worked with you until you could do it correctly on a consistent basis.
After my class and pool work, I did two ocean dives with the SSI group. The next day we went to a natural spring where the water was, let us say,,,umm, freezing. I declined to do those last two dives and got a referral letter for the next weekend.
I then went back out to the ocean with a PADI shop for my last two check out dives. Now this PADI instructor, rightfully so, had no real idea of what I knew and what skills I had. So, he asked if he could spend some time going through the course. I felt that was a good idea and agreed without hesitation. And that is when I learned that the PADI course is not nearly as intense as the SSI course, at least not at this shop with this instructor. The demands were significantly less stringent in that I didnt have to know any of the safety skills SSI taught me. Things like emergency ascents, buddy assisted ascents, search and rescue, towing a disabled diver to shore (or the boat), buddy breathing and a couple other skills. At SSI, we had to swim 12 laps in an olympic pool and then immediately tread water for 15 minutes and then immediately float for 5 minutes. I remember that distinctly because I came within an iota of quitting the whole thing about 15 times that night. All without a wetsuit.
At Padi, they did the swim in the pool but didnt have to tread water until they were in the ocean and wearing wetsuits. I did the tread water/float test again for the PADI guy and being in the ocean and wearing a wetsuit, I darn near fell asleep waiting for the time to expire. With a wetsuit and in salt water, I could not sink if I tried. That seemed like a fruitless test, if you ask me but who's asking.
Just my opinion and all those who stated it may be the instructor moreso than the course itself could be 100% correct. All I know is, my personal experience has proven SSI to appear much more difficult. And now that I have passed it, I am glad I took the most intense of the two.
Perhaps I should mention that the SSI training shop also certified me with NAUI so maybe that made a difference but I dont think so. Anyway, I am SSI and NAUI OW certified.
The lone complaint I have is that neither spent the necessary time to properly teach me buoyancy control. I think that should be a must; but then again, I think sign should be incorporated also. (sign = speaking by forming letters and words with your hands as deaf people do to communicate)