Well, you don't know where you want to work. PADI is the most widespread organisation. So if you do PADI, then odds are wherever you wind up will have a PADI shop. If not it's fairly easy to crossover from PADI to most of the other big training agencies if need be. Just playing the percentages
Actually that is incorrect because as tstormdiver stated an SSI Dive Con is a combonation of the equivilant PADI Divemaster and Assistant Instructor. It would be better to go SSI up to Dive Con and then cross over to PADI if you really wanted to become a PADI professional. I have been looking at this because the shop I now spend most of my time at is SSI/ANDI and I am a PADI Divemaster. Crossing over for me would not really be worth the effort without the additional training to be a Dive Con.