So just following up my my earlier post. I took both PADI's and SSI's respective rescue courses. In summary, SSI focuses more on prevention, while PADI focuses more on rescue. Physically, the PADI class was much more demanding. There are some significant differences in terms of rescue breathing for an unconscious diver where you are a long ways from shore (assuming you are willing to provide mouth to mouth). PADI teaches that if you are within 5 minutes of shore, you do a rescue breath every 5 seconds. SSI says if you are longer than a short distance (undefined), then you do rescue breaths. My SSI instructor told me that SSI used to do it the same way as PADI just a few years ago. I don't want to start a debate on which is better. If I was to choose only one course, I'd take the PADI one, as it is tougher. But I'd recommend taking both if you have the time/budget/interest. I'm big on safety and learning. I think it will be a while before I stop taking classes, as since my OW course, I've had some good instructors from both PADI and SSI (I do plan on taking classes from SDI and TDI in the future as well, but after I get over 100 dives, and I'm about half way there).
