If designed properly, dual rails will work just like single rail.
The PSUs are fairly equivalent. One is made by Delta and the other by Seasonic. Both are fairly decent - not the best in the world, but solid enough.
Maybe use the one with the higher +12v? For the dual rail, look up the "combined" power.
The best way to future-proof is to save money and spend it on future products. (Ken g6)
SSD turns duds into studs. (JBT)