Hi again,
just saw this link about Padi and SSI, thought I share with you, as I got some pm's ref the difference of the agencies
http://www.dive-cairns.com/padissi.shtml
in general, all Padi, SSI, or NAUI are internationally registered and you can dive with all anywhere you want to go. More important than the agency is the dive shop / the people / the instructor you go with, and having someone you feel comfortable with.
Especially PADI and SSI won't make much of a diference when you first start your diving.... the difference gets a bit more when you get to Advanced, where SSI will have few more requirement (more dives) than PADI.. which I think is a good thing, as they make sure you get the experience to be advanced...
in the end, it's important you feel comfortalbe at the shop and agency you're with. I am with SSI and very very happy there.....