My understanding is that you are asking about employment prospects rather than training standards--is that right? (Because I have no interest in participating in any discussion that involves "best" in regard to training.)
Both SSI and PADI have a strong international presence, so getting a job because of agency affiliation is not a critical issue when deciding between these two in many parts of the world. If there is a part of the world where you are yearning to work, find out whether there is a huge disparity in market share amongst the various agencies. Here in SE Asia, for example, there are extremely limited opportunities for NAUI professionals. The same can be said for SDI. SSI is slowly but steadily gaining market share in the region, and many shops are both PADI and SSI at the moment. PADI enjoys the overwhelming majority of market share in the region.
The bigger employment issue, from my perspective, is that it's hard for a foreign dive pro who has only a DM ticket to get legal work. In Thailand, for example, foreigners must have instructor ratings in order to qualify for a work permit, even if all they do is lead dives.
Now, if I've read your post wrong and all you want to do is fun diving, well, then, there is no issue at all. Any cert works as well as the other for going diving.