It's a tough decision, the extra aid slot can be a big help for Tech deals and for supplying emergency aid.
If you purchase the Disaster Relief Agency instead of the Social security System, it will be 30 days before you get to choose again. So what would you lose ?
SSS Income = 368,053.54 * 30 = 11,041,606.20
DRA Income = 154,582.49 * 30 = 4,637,474.70
So theoretically by choosing the DRA over the SSS you would lose 6,404,131.5 in revenue over the next 30 days.
That 6 million would pay for 200 tech in tech deals, or 65 infrastructure points (with the current 3 factories).
So what would the extra aid slot be worth in the next 30 days I here you ask
Well using the slot for a tech deal would get you 100 tech for 3 mill during the next 30 days. Buying 100 Tech outside a tech deal would cost you 16,331,680 for a potential saving of 13,331,680.
So are you buying tech outside of tech deals is the question ?
If so then undoubtedly the DRA is a much better proposition than the SSS. You would make 6 mill from owning the DRA and save 13 mill on 100 tech for a total benefit of 19 mill which is 8 mill more than you would make from the SSS.
Of course would you really be wasting that much money buying tech ?
The general rule most people use is as Kahn says Stock Market, SSS, and Interstate if you are buying infrastructure regularly (it may be worth holding off on the Interstate wonder until you are ready for the 8k jump, still researching that
Exceptions are sometimes made in the event of war to get a military wonder, also the National Research Lab is a good counter for the Border Walls improvement.
@Kahn Are you sure about that ? from my reading the DRA gives an extra aid slot just like the Harbor gives you an extra trade slot. The Federal Aid Commission which raises the cap on aid by 50% requires both parties to have the wonder.